lmb: Remove imx board_lmb_reserve()

lmb: Remove imx board_lmb_reserve()

This function is clearly architecture specific code, not board specific
code. The only difference from the previous arm arch_lmb_reserve() is the
extra reservation of 16k of memory below the stack bottom, rather than
the 4k. The common code now also uses 16k alignment. Remove this custom
implementation, as it now behaves exactly as the common code.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Alexey Brodkin <alexey.brodkin@synopsys.com>
Cc: Angelo Dureghello <angelo@sysam.it>
Cc: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
Cc: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Cc: Hai Pham <hai.pham.ud@renesas.com>
Cc: Michal Simek <monstr@monstr.eu>
Cc: Simon Goldschmidt <simon.k.r.goldschmidt@gmail.com>
Cc: Tom Rini <trini@konsulko.com>
Cc: Wolfgang Denk <wd@denx.de>
Cc: Ye Li <ye.li@nxp.com>