UPSTREAM: arm64: KVM: Remove weak attributes

As we've now switched to the new world switch implementation,
remove the weak attributes, as nobody is supposed to override
it anymore.

Acked-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
(cherry picked from commit 3ffa75cd)
Signed-off-by: Alex Shi <alex.shi@linaro.org>
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>