AArch64: Calculate private_handle_t's numInts

AArch64: Calculate private_handle_t's numInts

A constant sNumInts with a value of 6 was being assigned to the numInts
attribute in the private_handle_t constructor, and was also used in the
validate method. That constant value is appropriate for 32-bit systems
but is not appropriate for a 64-bit system where uintptr_t used for
base attribute will be 64-bit.

sNumInts is now changed to a static inline function that calculates
numInts.

Change-Id: I482ddb5915c9ff55fb2e2a87887a0ec2dc2299ed
Signed-off-by: Marcus Oakland <marcus.oakland@arm.com>
Signed-off-by: Ashok Bhat <ashok.bhat@arm.com>