x86/HVM: EOI handling function adjustments

x86/HVM: EOI handling function adjustments

The vector parameters are more usefully u8 right away. This is
particularly important for the vioapic_update_EOI() invocation from
vioapic_write() (which luckily is only a latent issue, as
VIOAPIC_VERSION_ID is still hard coded to 0x11 right now). But it at
once allows simplifying VMX's EXIT_REASON_EOI_INDUCED handling (the
kind of pointless helper function should have been static anyway; not
being use for anything else, it gets removed altogether).

Plus vlapic_handle_EOI() (now renamed for that purpose) can be used as
the tail of vlapic_EOI_set() instead of duplicating that code.

Finally replace a stray current->domain use in vlapic_handle_EOI().

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>