KVM: SVM: Use asm goto to handle unexpected #UD on SVM instructions

Add svm_asm*() macros, a la the existing vmx_asm*() macros, to handle
faults on SVM instructions instead of using the generic __ex(), a.k.a.
__kvm_handle_fault_on_reboot().  Using asm goto generates slightly
better code as it eliminates the in-line JMP+CALL sequences that are
needed by __kvm_handle_fault_on_reboot() to avoid triggering BUG()
from fixup (which generates bad stack traces).

Using SVM specific macros also drops the last user of __ex() and the
the last asm linkage to kvm_spurious_fault(), and adds a helper for
VMSAVE, which may gain an addition call site in the future (as part
of optimizing the SVM context switching).

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20201231002702.22237077

-8-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>