dt-bindings: mfd: qcom-spmi-pmic: Add PMI632 compatible

Document support for the pmi632, often found with the sdm632 SoC.

Signed-off-by: Luca Weiss <luca@z3ntu.xyz>
Acked-by: Pavel Machek <pavel@ucw.cz>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20230414-pmi632-v2-5-98bafa909c36@z3ntu.xyz