x86/hpet: Don't enable legacy replacement mode unconditionally

x86/hpet: Don't enable legacy replacement mode unconditionally

Commit e1de4c196a2e ("x86/timer: Fix boot on Intel systems using ITSSPRC
static PIT clock gating") was reported to cause boot failures on certain
AMD Ryzen systems.

Refine the fix to do nothing in the default case, and only attempt to
configure legacy replacement mode if IRQ0 is found to not be working.  If
legacy replacement mode doesn't help, undo it before falling back to other IRQ
routing configurations.

In addition, introduce a "hpet" command line option so this heuristic
can be overridden.  Since it makes little sense to introduce just
"hpet=legacy-replacement", also allow for a boolean argument as well as
"broadcast" to replace the separate "hpetbroadcast" option.

Reported-by: Frédéric Pierret frederic.pierret@qubes-os.org
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Tested-by: Frédéric Pierret <frederic.pierret@qubes-os.org>