KVM: x86/pmu: Check eventsel first when emulating (branch) insns retired

When triggering events, i.e. emulating PMC events in software, check for
a matching event selector before checking the event is allowed.  The "is
allowed" check *might* be cheap, but it could also be very costly, e.g. if
userspace has defined a large PMU event filter.  The event selector check
on the other hand is all but guaranteed to be <10 uops, e.g. looks
something like:

   0xffffffff8105e615 <+5>:	movabs $0xf0000ffff,%rax
   0xffffffff8105e61f <+15>:	xor    %rdi,%rsi
   0xffffffff8105e622 <+18>:	test   %rax,%rsi
   0xffffffff8105e625 <+21>:	sete   %al

Link: https://lore.kernel.org/r/20231110022857.1273836-10-seanjc@google.com


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