KVM: arm64: Move kern_hyp_va() usage in __load_guest_stage2() into the callers

It is a bit awkward to use kern_hyp_va() in __load_guest_stage2(),
specially as the helper is shared between VHE and nVHE.

Instead, move the use of kern_hyp_va() in the nVHE code, and
pass a pointer to the kvm->arch structure instead. Although
this may look a bit awkward, it allows for some further simplification.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Jade Alglave <jade.alglave@arm.com>
Cc: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20210806113109.2475-4-will@kernel.org