ARM: PL011: Allow better handling of vendor data

Rather than copying all vendor data into the port structure, copy
just that which is frequently used, and keep a pointer to the
remaining vendor data structure.  This makes it easier to add
vendor quirks in the future.

Acked-by: Linus Walleij <linus.walleij@stericsson.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>