mfd: wm8997: Make Kconfig prompt for WM8997 more consistent

The Kconfig prompt for WM8997 says "Support for..." while the other MFD
Kconfigs (including the adjacent ones for other Arizona devices) just
list the device name which sticks out like a sore thumb when doing
configuration.

Signed-off-by: Mark Brown <broonie@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>