Platform/Sgi: Update Cache Coherency Attribute value of Root Complex

As SBSA requires root complexes to support IO Coherency and to
be in the same shareability domain as the CPUs, update CCA's value
to be equal to EFI_ACPI_IORT_MEM_ACCESS_PROP_CCA.

Signed-off-by: Chaitanya S Prakash <ChaitanyaS.Prakash@arm.com>
Change-Id: I758e39781c9f6ec4634fad834debdccde10ac58a