x86/platform/intel-mid: Rename mrfl.c to mrfld.c

x86/platform/intel-mid: Rename mrfl.c to mrfld.c

Use mrfld as an abbreviation of Merrifield to be consistent with the rest of
the code.

In the future we are going to add more files here prefixed with 'mrfld'.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1466265094-146113-1-git-send-email-andriy.shevchenko@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>