IOMMU/x86: work around bogus gcc12 warning in hvm_gsi_eoi()

IOMMU/x86: work around bogus gcc12 warning in hvm_gsi_eoi()

As per [1] the expansion of the pirq_dpci() macro causes a -Waddress
controlled warning (enabled implicitly in our builds, if not by default)
tying the middle part of the involved conditional expression to the
surrounding boolean context. Work around this by introducing a local
inline function in the affected source file.

Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>
[1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102967