ARM: 6295/1: fix U300 apb_pclk split

This fixes a regression due to the new apb_pclk stuff in the U300
platform, makes it run by splitting the apb clock off the single
UART clocks. For the MMCI and PL022 clocks we don't split them:
these are actually hardwired to the same clock terminal and will
thus simply have a double reference count and will be referenced
twice.

We also move clock registration to .init_irq() so they are
available early enough for probing to be successful and remove the
earlier quirk to clock primecells during PrimeCell registration.

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