asm-generic: relaxed.h: defined relaxed.h

Defined a new header file relaxed.h, which contains basic
macros which will be used for improving power efficiency for
arm64.

bug 1440421

Signed-off-by: Sumit Singh <sumsingh@nvidia.com>
GVS: Gerrit_Virtual_Submit
Reviewed-by: Bharat Nihalani <bnihalani@nvidia.com>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>