arm64: Convert ID_AA64MMFR0_EL1.TGRAN{4,16,64}_2 to UnsignedEnum

arm64: Convert ID_AA64MMFR0_EL1.TGRAN{4,16,64}_2 to UnsignedEnum

ID_AA64MMFR0_EL1.TGRAN{4,16,64}_2 are currently represented as unordered
enumerations. However, the architecture treats them as Unsigned,
as hinted to by the MRS data:

(FEAT_S2TGran4K <=> (((UInt(ID_AA64MMFR0_EL1.TGran4_2) == 0) &&
		       FEAT_TGran4K) ||
		     (UInt(ID_AA64MMFR0_EL1.TGran4_2) >= 2))))

and similar descriptions exist for 16 and 64k.

This is also confirmed by D24.1.3.3 ("Alternative ID scheme used for
ID_AA64MMFR0_EL1 stage 2 granule sizes") in the L.b revision of
the ARM ARM.

Turn these fields into UnsignedEnum so that we can use the above
description more or less literally.

Reviewed-by: Fuad Tabba <tabba@google.com>
Tested-by: Fuad Tabba <tabba@google.com>
Link: https://patch.msgid.link/20251210173024.561160-3-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>