Previously, data caches were disabled while enabling MMU only because of
active stack. Now that we can enable MMU without using stack, we can
enable both MMU and data caches at the same time.

Change-Id: I73f3b8bae5178610e17e9ad06f81f8f6f97734a6
Signed-off-by: Jeenu Viswambharan <jeenu.viswambharan@arm.com>