[ARM] Add rtc-cmos driver for ISA-based footbridge platforms

... but the rtc-cmos is rather broken; if PNP is enabled, it assumes
that we have ACPI (!) which is quite bogus on these platforms -
which may have ISAPNP but not ACPI.  Something to be solved in the
future.

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