armv8: mmu: remove unused macro definition

Macro VA_BITS and PTE_BLOCK_BITS are not used
in the code, so remove them.

Signed-off-by: Andy Yan <andy.yan@rock-chips.com>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reviewed-by: York Sun <york.sun@nxp.com>