ARM: debug: provide generic option choices for 8250 and PL01x ports

Provide generic option choices for 8250 and PL01x UART ports; these can
now be selected by UART type rather than asking about the platform.
This means that a kernel configuration user can manually choose the
various parameters of the debug UART without resorting to the platform
having to encode the possible settings.

These two generic options are preferred over further debug entries for
these ports; the existing options which refer back to the 8250 and PL01x
ports are now considered deprecated.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>