spm: enable sve for non secure and secure world

SVE is enabled by default on the FVP. The access to the SVE registers
are disabled in BL31. The linux kernel, during boot, reads the status
register and tries to access it. This cause an exception during boot.

Enable SVE in BL31 to fix the issue.

Signed-off-by: Nishant Sharma <nishant.sharma@arm.com>
Change-Id: I87eda1f8e5155deb51c762636100cbb4e149a580