romlib: Allow patching of romlib functions

This change allows patching of functions in the
romlib. This can be done by adding "patch" at the
end of the jump table entry for the function that
needs to be patched in the file jmptbl.i.
Functions patched in the jump table list will be
built as part of the BL image and the romlib
version will not be used

Change-Id: Iefb200cb86e2a4b61ad3ee6180d3ecc39bad537f
Signed-off-by: Sathees Balya <sathees.balya@arm.com>