rtc: pl031: use per-vendor variables for special init

Instead of hard-checking for certain vendor codes, follow the pattern of
other AMBA (PrimeCell) drivers and use variables in the vendor data.
Get rid of the locally cached vendor and hardware revision since we
already have the nice vendor data variable in the state.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>