fix(mask): remove system registers XXX_MASK definitions

This patch removes XXX_MASK definitions for system registers
bit fields which are replaced by MASK(XXX) macro used directly.
Masking and shifting operations are replaced with
INPLACE() and EXTRACT() macros.
XXX_BIT macros which were defined via INPLACE(XX, 1) are
replaced with (UL(1) << N) definitions, and their XXX_SHIFT
and XXX_WIDTH macros are removed to improve readability
and reduce code size.
This patch also fixes bug in duplicated declaration for
read_ID_AA64MMFR2_EL1() function in arch_helpers.c.

Signed-off-by: AlexeiFedorov <Alexei.Fedorov@arm.com>
Change-Id: Ife64413c45711ba39b043cdc3510cf90fca0cfb6