ARM: ux500: solve some Kconfig mess

First rename the config option MACH_U8500 to MACH_MOP500
because that is what it's obviously all about, this has
confused me for the last time. Fix some whitespace in the
process.

Since the machine descriptors for HREFv60 and snowball
are clearly in the file board-mop500.c which only
compiles if MACH_MOP500 (former MACH_U8500) is set,
select this for the board variants and nothing else.

For the MOP500 variants the UIB (user interface board)
is probed using I2C so select I2C and I2C_NOMADIK so
we know that this probe will always be successful.

Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>