AFF3 bits of MPIDR corresponds to Chip-Id in Arm multi-chip platforms.
For calculating linear core position of CPU cores from slave chips, AFF3
bits has to be used. Update `plat_arm_calc_core_pos` assembly function
to include AFF3 bits in calculation.

Change-Id: I4af2bd82ab8e31e18bc61de22705a73893954260
Signed-off-by: Vijayenthiran Subramaniam <vijayenthiran.subramaniam@arm.com>