[PATCH] arm64: entry: fix BACKPORT "use ldp/stp instead of push/pop.."

This fixes LSK's backport of Will Deacon's commit:
"BACKPORT: arm64: entry: use ldp/stp instead of push/pop when
saving/restoring regs"

Signed-off-by: Jorge Ramirez-Ortiz <jorge.ramirez-ortiz@linaro.org>
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>