ARMv7: Mark the PTWs inner WBWA on SMP and WB on UP

There are additional bits to set for the ARMv7 SMP extensions in the
TTBR registers. The IRGN bits order is counter-intuitive but it allows
software built for the ARMv7 base architecture to run on an
implementation with the MP extensions.

Signed-off-by: Tony Thompson <Anthony.Thompson@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>