There are three calls to mmap_add_region() that always occur in
arm_setup_page_tables(), and two further calls based on whether coherent
memory is enabled, and whether SPM is enabled in BL31.

This commit adapts the ARM_BL_REGIONS definition to match the number of
calls made inside arm_setup_page_tables() so that the MAX_MMAP_REGIONS
is realigned with what is actually occurring.

Change-Id: I7adc05951abccf2cbd5c86280eb874911e6a1566
Signed-off-by: Chris Kay <chris.kay@arm.com>