x86: Always inline context_tracking_guest_enter()

Yes, it really did out-of-line this....

vmlinux.o: warning: objtool: vmx_vcpu_enter_exit()+0x31: call to context_tracking_guest_enter() leaves .noinstr.text section

000000000019f660 <context_tracking_guest_enter>:
  19f660:	e8 00 00 00 00       	callq  19f665 <context_tracking_guest_enter+0x5>	19f661: R_X86_64_PLT32	__sanitizer_cov_trace_pc-0x4
  19f665:	31 c0                	xor    %eax,%eax
  19f667:	c3                   	retq

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210624095148.003928226@infradead.org