juno: Add romlib support

This patch adds support to build a combined BL1
and ROMLIB binary file with the right page
alignment in Juno. When USE_ROMLIB=1 is set for
Juno, it generates the combined file
bl1_romlib.bin which needs to be used instead of
bl1.bin

Change-Id: I407efbe48d3e522fa6ef855538a9587193cb1919
Signed-off-by: Sathees Balya <sathees.balya@arm.com>