KVM: VMX: Move vCPU-run code to a proper assembly routine

As evidenced by the myriad patches leading up to this moment, using
an inline asm blob for vCPU-run is nothing short of horrific.  It's also
been called "unholy", "an abomination" and likely a whole host of other
names that would violate the Code of Conduct if recorded here and now.

The code is relocated nearly verbatim, e.g. quotes, newlines, tabs and
__stringify need to be dropped, but other than those cosmetic changes
the only functional changees are to add the "call" and replace the final
"jmp" with a "ret".

Note that STACK_FRAME_NON_STANDARD is also dropped from __vmx_vcpu_run().

Suggested-by: Andi Kleen <ak@linux.intel.com>
Suggested-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>