fix instruction address range limitation

fix instruction address range limitation

For the adr instruction, it require the label's offset from the
address of this instruction must be in the range +/-1MB. If the
option "BL2_IN_XIP_MEM" is set to '1', in some cases, BL2's RW
memory will not in the range of +/-1MB from BL2's RO memory region.
so we need to use ldr instruction to cover this case.

Signed-off-by: Jiafei Pan <Jiafei.Pan@nxp.com>