Calculate TCR bits based on VA and PA

Currently the TCR bits are hardcoded in xlat_tables.c. In order to
map higher physicall address into low virtual address, the TCR bits
need to be configured accordingly.

This patch is to save the max VA and PA and calculate the TCR.PS/IPS
and t0sz bits in init_xlat_tables function.
Magic number 0xFFFF000000000000UL. Create a #define (if one doesn't already exist). Same for other magic numbers in this file.