fix(gicv3): restore scr_el3 after changing it

EL3's context is poorly defined as it is and polluting it further is not
a good idea. Put it back as it was before the function call.

Signed-off-by: Boyan Karatotev <boyan.karatotev@arm.com>
Change-Id: I9d13c9517962b501246989fd2126d08410191784
1 file changed