x86/msi: Consolidate HPET allocation

None of the magic HPET fields are required in any way.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Joerg Roedel <jroedel@suse.de>
Link: https://lore.kernel.org/r/20200826112331.943993771@linutronix.de