ppc: lmb: move arch specific lmb reservations to arch_misc_init()

ppc: lmb: move arch specific lmb reservations to arch_misc_init()

All the current function definitions of arch_lmb_reserve() are doing
the same thing -- reserve the U-Boot memory region. The powerpc(ppc)
architecture, in addition, is making some LMB reservations for the
bootm related image loading. Move these ppc specific reservations to
the arch_misc_init() function. This allows to move the U-Boot memory
region reservation to a different function, and remove
arch_lmb_reserve() in a subsequent commit.

Signed-off-by: Sughosh Ganu <sughosh.ganu@linaro.org>
Reviewed-by: Simon Glass <sjg@chromium.org>