xen/x86: cleanup unused NMI/MCE code

xen/x86: cleanup unused NMI/MCE code

pv_raise_interrupt() is only called for NMIs these days, so the MCE
specific part can be removed. Rename pv_raise_interrupt() to
pv_raise_nmi() and NMI_MCE_SOFTIRQ to NMI_SOFTIRQ.

Additionally there is no need to pin the vcpu which the NMI is delivered
to; that is a leftover of (already removed) MCE handling. So remove the
pinning, too. Note that pinning was introduced by commit 355b0469a8
adding MCE support (with NMI support existing already). MCE using that
pinning was removed with commit 3a91769d6e again without cleaning up the
code.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-and-tested-by: Andrew Cooper <andrew.cooper3@citrix.com>