ARM: rmobile: Add TPL support on R8A7791 M2 Porter

ARM: rmobile: Add TPL support on R8A7791 M2 Porter

Add and enable TPL on M2 Porter. The TPL must fit into 16 kiB due
to the Gen2 BootROM restriction. The TPL is running from MERAM and
is capable of performing the initial initialization of PFC, Clock,
GPIO, LBSC, DBSC and QSPI NOR. DBSC is responsible for bringing up
the DDR DRAM access. The TPL is capable of loading the next stage,
U-Boot, from either SPI NOR or UART as a fallback. If either does
provide a valid U-Boot uImage, the system stops, which allows the
operator to load U-Boot ie. via JTAG and start it manually.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>