Platform setup code has to reserve some memory for storing the
memory layout information. It is populated in early platform setup
code.
blx_get_sec_mem_layout() functions used to return a copy of this
structure. This patch modifies blx_get_sec_mem_layout() functions
so that they now directly return a pointer to their memory layout
structure. It ensures that the memory layout returned by
blx_get_sec_mem_layout() is always up-to-date and also avoids a
useless copy of the meminfo structure.
Also rename blx_get_sec_mem_layout() to blx_plat_sec_mem_layout()
to make it clear those functions are platform specific.
Change-Id: Ic7a6f9d6b6236b14865ab48a9f5eff545ce56551