[MIPS] Delete now-unreferenced i2c-yosemite.h header file.

Given that the corresponding source file i2c-yosemite.c file was
removed in commit daa4a68f, and that
no one else includes this file, it seems safe to delete it.

Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>