regulator: REGULATOR_QCOM_REFGEN should depend on ARCH_QCOM

The Qualcomm MMIO-mapped reference voltage regulator is only present on
Qualcomm SoCs.  Hence add a dependency on ARCH_QCOM, to prevent asking
the user about this driver when configuring a kernel without Qualcomm
SoC support.

Fixes: 7cbfbe23 ("regulator: Introduce Qualcomm REFGEN regulator driver")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/60938ed138c9331ba3d2891fbd3b3d6644d3fbdc.1690300012.git.geert+renesas@glider.be


Signed-off-by: Mark Brown <broonie@kernel.org>