Kconfig: Change SYS_MALLOC_F_LEN default to 0x2000

Kconfig: Change SYS_MALLOC_F_LEN default to 0x2000

The most commonly used value today is 0x2000 and not 0x400.  Rework the
Kconfig logic to use this more frequently used value as the default.

Cc: Andrew F. Davis <afd@ti.com>
Cc: Alex Nemirovsky <alex.nemirovsky@cortina-access.com>
Cc: Alexey Brodkin <abrodkin@synopsys.com>
Cc: Alison Wang <alison.wang@nxp.com>
Cc: Anastasiia Lukianenko <anastasiia_lukianenko@epam.com>
Cc: Andes <uboot@andestech.com>
Cc: Andre Przywara <andre.przywara@arm.com>
Cc: Bharat Gooty <bharat.gooty@broadcom.com>
Cc: David Lechner <david@lechnology.com>
Cc: Dzmitry Sankouski <dsankouski@gmail.com>
Cc: Enric Balletbo i Serra <eballetbo@gmail.com>
Cc: Eugeniy Paltsev <paltsev@synopsys.com>
Cc: Fabio Estevam <festevam@gmail.com>
Cc: Gerald Kerma <dreagle@doukki.net>
Cc: Gregory CLEMENT <gregory.clement@bootlin.com>
Cc: Holger Brunck <holger.brunck@hitachienergy.com>
Cc: Jaehoon Chung <jh80.chung@samsung.com>
Cc: Jassi Brar <jaswinder.singh@linaro.org>
Cc: Kristian Amlie <kristian.amlie@northern.tech>
Cc: Krzysztof Kozlowski <krzk@kernel.org>
Cc: Liviu Dudau <liviu.dudau@foss.arm.com>
Cc: Luka Perkov <luka.perkov@sartura.hr>
Cc: Lukasz Majewski <lukma@denx.de>
Cc: Marek Vasut <marex@denx.de>
Cc: Masami Hiramatsu <masami.hiramatsu@linaro.org>
Cc: Matthias Brugger <mbrugger@suse.com>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Michael Walle <michael@walle.cc>
Cc: Michal Simek <michal.simek@xilinx.com>
Cc: Minkyu Kang <mk7.kang@samsung.com>
Cc: Nikita Kiryanov <nikita@compulab.co.il>
Cc: Nobuhiro Iwamatsu <nobuhiro.iwamatsu.yj@renesas.com>
Cc: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Cc: Otavio Salvador <otavio@ossystems.com.br>
Cc: Patrice Chotard <patrice.chotard@foss.st.com>
Cc: Paul Burton <paul.burton@mips.com>
Cc: Paul Kocialkowski <contact@paulk.fr>
Cc: Priyanka Jain <priyanka.jain@nxp.com>
Cc: Rajesh Bhagat <rajesh.bhagat@nxp.com>
Cc: Rayagonda Kokatanur <rayagonda.kokatanur@broadcom.com>
Cc: Sergey Temerkhanov <s.temerkhanov@gmail.com>
Cc: Simon Glass <sjg@chromium.org>
Cc: Stefan Bosch <stefan_b@posteo.net>
Cc: Stephan Gerhold <stephan@gerhold.net>
Cc: Tetsuyuki Kobayashi <koba@kmckk.co.jp>
Cc: Thomas Chou <thomas@wytron.com.tw>
Cc: Thomas Fitzsimmons <fitzsim@fitzsim.org>
Cc: Thomas Weber <weber@corscience.de>
Cc: Tony Dinh <mibodhi@gmail.com>
Cc: Trevor Woerner <twoerner@gmail.com>
Cc: Vitaly Andrianov <vitalya@ti.com>
Cc: Vladimir Zapolskiy <vz@mleia.com>
Cc: liuhao <liuhao@phytium.com.cn>
Cc: lixinde <lixinde@phytium.com.cn>
Cc: shuyiqi <shuyiqi@phytium.com.cn>
Cc: weichangzheng <weichangzheng@phytium.com.cn>
Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Thomas Chou <thomas@wytron.com.tw>
Reviewed-by: Masami Hiramatsu <masami.hiramatsu@linaro.org>
Reviewed-by: Tony Dinh <mibodhi@gmail.com>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>
Reviewed-by: Kristian Amlie <kristian.amlie@northern.tech>