MISRA cleanup in mem_region and semihosting files

MISRA defect cleanup and general code cleanup in mem_region.c and
semihosting.c.  This task also called for cleanup of the ARM NOR flash
driver but that was removed at some point since the Jira task was
created.  This patch fixes all MISRA defects in these files except for a
few "Calling function "console_flush()" which returns error information
without testing the error information." errors which can't really be
avoided.

Defects Fixed

File                           Line Rule
lib/semihosting/semihosting.c  70   MISRA C-2012 Rule 14.4 (required)
lib/semihosting/semihosting.c  197  MISRA C-2012 Rule 14.3 (required)
lib/semihosting/semihosting.c  210  MISRA C-2012 Rule 14.4 (required)
lib/utils/mem_region.c         128  MISRA C-2012 Rule 12.1 (advisory)

Signed-off-by: John Powell <john.powell@arm.com>
Change-Id: I21a039d1cfccd6aa4301da09daec15e373305a80