ARM: debug: move davinci debug to generic 8250 code

Davinci's debugging is just a copy of the old 8250_32 code with a
different base address.  Incorporate this into the generic 8250
debug code.

Acked-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>