Add support for the EFI/DIG PCDP console discovery table (see
http://www.dig64.org/specifications/DIG64_HCDPv20_042804.pdf).

This moves the code from drivers/serial/8250_hcdp.[ch] to
drivers/firmware/pcdp.[ch], since it's no longer 8250-specific.  It also
obsoletes CONFIG_SERIAL_8250_HCDP, replacing it with CONFIG_EFI_PCDP (which
defaults to Y for ia64).

In a nutshell, HCDP tells us "these UARTs are available for use as a
console," and it's up to the user to explicitly specify the console device.
 The kernel can guess in some cases, but not all.

The PCDP (aka HCDP v2) tells us what we really want to know, namely, "this
UART or VGA device is the console device." (It also has provision for
support for new device types.)
Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>