arm64: hyp-stub: Don't save lr in the EL1 code

The EL2 code is not corrupting lr anymore, so don't bother preserving
it in the EL1 trampoline code.

Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <cdall@linaro.org>