KVM: x86/mmu: Avoid indirect call for get_cr3

KVM: x86/mmu: Avoid indirect call for get_cr3

[ Upstream commit 2fdcc1b324189b5fb20655baebd40cd82e2bdf0c ]

Most of the time, calls to get_guest_pgd result in calling
kvm_read_cr3 (the exception is only nested TDP).  Hardcode
the default instead of using the get_cr3 function, avoiding
a retpoline if they are enabled.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Mathias Krause <minipli@grsecurity.net>
Link: https://lore.kernel.org/r/20230322013731.102955-2-minipli@grsecurity.net
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Mathias Krause <minipli@grsecurity.net>	# backport to v6.1.x
Signed-off-by: Sasha Levin <sashal@kernel.org>