ANDROID: arm64: Add support for system cache memory type

Non-coherent devices on systems that support a system or
last level cache may want to request that allocations be
cached in the system cache. For memory that is allocated
by the kernel, and used for DMA with devices, the memory
attributes used for CPU access should match the memory
attributes that will be used for device access.

The memory attributes that need to be programmed into
the MAIR for system cache usage are:

0xf4 - Normal memory, outer write back read/write allocate,
inner non-cacheable.

There is currently no support for this memory attribute for
CPU mappings, so add it.

Bug: 189339242
Change-Id: I3abc7becd408f20ac5499cbbe3c6c6f53f784107
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>
Signed-off-by: Georgi Djakov <quic_c_gdjako@quicinc.com>