misc/pvpanic: deduplicate common code

[ Upstream commit c1426d39 ]

pvpanic-mmio.c and pvpanic-pci.c share a lot of code.
Refactor it into pvpanic.c where it doesn't have to be kept in sync
manually and where the core logic can be understood more easily.

No functional change.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Link: https://lore.kernel.org/r/20231011-pvpanic-cleanup-v2-1-4b21d56f779f@weissschuh.net


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Stable-dep-of: ee59be35 ("misc/pvpanic-pci: register attributes via pci_driver")
Signed-off-by: Sasha Levin <sashal@kernel.org>