acpi: Narrow workaround for broken interrupt settings on x86

Commit 9a7bf07ccdc1 from 2016 introduced a workaround for some broken
BIOSes that specified active-lo instead of active-hi polarity for ISA
IRQs for UARTs. The workaround assumed that edge-sensitive ISA IRQs
on x86 should always be active-hi. However, some recent AMD systems
actually use active-lo edge-sensitive ISA IRQs (and not just for
UARTs, but also for the keyboard and PS/2 mouse devices) and the
override causes interrupts to be dropped resulting in boot time hangs,
non-working keyboards, etc.

Add a hw.acpi.override_isa_irq_polarity tunable (readable as a sysctl
post-boot) to control this quirk. It can be set to 1 to force enable
the override and 0 to disable it. The log of original message
mentions an Intel motherboard as the sample case, so default the
tunable to 1 on systems with an Intel CPU and 0 otherwise.

Special thanks to Matthias Lanter <freebsd@lanter-it.ch> for tracking
down boot time issues on recent AMD systems to mismatched interrupt
polarity.

PR: 270707
Reported by: aixdroix_OSS@protonmail.com, Michael Dexter
Reported by: mfw_burn@pm.me, Hannes Hfauswedell <h2+fbsdports@fsfe.org>
Reported by: Matthias Lanter <freebsd@lanter-it.ch>
Reported by: William Bulley <web@umich.edu>
Reviewed by: imp, emaste
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D45554

(cherry picked from commit 0a34d050ae8ea14feddd3d2a62fd2f612613b2c5)