regulator: onsemi-ncp6335d: add support for tlmm spare register control

Certain Qualcomm chips mux the output of some GPIOs using the TLMM_SPARE
register. Add support for a device tree property which can be used to
specify a mask and value to write into this register so that the VSEL GPIO
can be toggled successfully on affected devices. When the appropriate bits
in the TLMM_SPARE register are written, the physical output of the GPIO can
be controlled normally via GPIO control registers.

Change-Id: Ic8a0886886a44687931ab5cb8150383cd84db2f6
Signed-off-by: Ke Liu <keliu@codeaurora.org>