mfd: Remove twelve unused Kconfig symbols

Twelve Kconfig symbols, all related to WM8350, WM8351, and WM8352, are
unused. Commit 19d57ed5

 ("mfd: Remove
custom wm8350 cache implementation") removed all their (actual) users.
Remove these symbols too.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>