Fix build by correcting asm helper function usage in TSPD

This patch fixes a regression failure due to the use of functions by the 
TSPD code which access system registers with partially qualified names. 
These functions had been removed in an earlier patch. The relevant code 
has been updated to access these registers with their fully qualified 
names.

Fixes ARM-software/tf-issues#119

Change-Id: Ide1bc5036e1b8164a42f7b7fe86186ad860e0ef9