arm64: fsl-layerscape: add get_svr and IS_SVR_REV helper

Adds get_svr and IS_SVR_REV helpers for ARMv8 platforms,
similar to PPC and ARMv7.

Signed-off-by: Sriram Dash <sriram.dash@nxp.com>
Signed-off-by: Rajesh Bhagat <rajesh.bhagat@nxp.com>