KVM: VMX: always_inline VMREADs

vmcs_readl() and friends are really short, but gcc thinks they are long because of
the out-of-line exception handlers.  Mark them always_inline to clear the
misunderstanding.

Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>