rtc: mrst: Remove driver for deprecated platform

rtc: mrst: Remove driver for deprecated platform

Intel Moorestown and Medfield are quite old Intel Atom based
32-bit platforms, which were in limited use in some Android phones,
tablets and consumer electronics more than eight years ago.

There are no bugs or problems ever reported outside from Intel
for breaking any of that platforms for years. It seems no real
users exists who run more or less fresh kernel on it. The commit
4f98b67df79b ("ASoC: Intel: remove mfld_machine") also in align
with this theory.

Due to above and to reduce a burden of supporting outdated drivers
we remove the support of outdated platforms completely.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>