[RESEND PATCH 0/7] serial: Add MMIO & SPCR support

[Benjamin Herrenschmidt]

This series adds support for MMIO serial ports and auto-configuration
via ACPI SPCR.

This is necessary for the serial port to work on AWS EC2 "metal" x86
systems.

An MMIO serial port can be specified explicitely using the
"mmio," prefix for the --port argument to the 'serial' command,
the register access size can also be specified via a suffix,
and when 'serial' is used without arguments, it will try to use
an ACPI SPCR entry (if any) to add the default port and configure
it appropriately (speed, parity etc...)

This was tested using SPCR on an actual c5.metal instance, and using
explicit instanciation via serial -p mmioXXXXXXXX on a modified qemu
hacked to create MMIO PCI serial ports.