misc/pvpanic: add PCI driver

Add support for pvpanic PCI device added in qemu [1]. At probe time, obtain the
address where to read/write pvpanic events and pass it to the generic handling
code. Will follow the same logic as pvpanic MMIO device driver. At remove time,
unmap base address and disable PCI device.

[1] https://github.com/qemu/qemu/commit/9df52f58e76e904fb141b10318362d718f470db2

Signed-off-by: Mihai Carabas <mihai.carabas@oracle.com>
Link: https://lore.kernel.org/r/1616597356-20696-4-git-send-email-mihai.carabas@oracle.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

misc/pvpanic: split-up generic and platform dependent code

Split-up generic and platform dependent code in order to be able to re-use
generic event handling code in pvpanic PCI device driver in the next patches.

The code from pvpanic.c was split in two new files:
- pvpanic.c: generic code that handles pvpanic events
- pvpanic-mmio.c: platform/bus dependent code

Signed-off-by: Mihai Carabas <mihai.carabas@oracle.com>
Link: https://lore.kernel.org/r/1616597356-20696-2-git-send-email-mihai.carabas@oracle.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>