hash: use armv8-a CRC32 instructions

hash: use armv8-a CRC32 instructions

armv8-a has optional CRC32 extension, march=armv8-a+crc enables code
generation for the ARMv8-A architecture together with
the optional CRC32 extensions.

added RTE_MACHINE_CPUFLAG_CRC32 to detect the availability of
CRC32  extension in compile time. At run-time, The RTE_CPUFLAG_CRC32
can be used to find the availability.

armv8-a+crc target support added in GCC 4.9,
Used inline assembly and emulated __ARM_FEATURE_CRC32 to work
with tool-chain < 4.9

Signed-off-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>