Remove useless copies of meminfo structures

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
Move RUN_IMAGE constant from bl1.h to bl_common.h

RUN_IMAGE constant is used by all bootloader stages.

Change-Id: I1b4e28d8fcf3ad1363f202c859f5efab0f320efe
BL2: Sanity check value in x0 in the entry point code

Change-Id: Icef68e314e6ba0f3694189b57f4b1dbbea5ba255
Make BL31's ns_entry_info a single-cpu area

ns_entry_info used to be a per-cpu array.  This is a waste of space
because it is only accessed by the primary CPU on the cold boot path.
This patch reduces ns_entry_info to a single-cpu area.

Change-Id: I647c70c4e76069560f1aaad37a1d5910f56fba4c