dt-bindings: leds: qcom-lpg: Add compatible for PMI632 LPG block

Document the availability of an LPG configuration for the PMI632 PMIC in
the Qualcomm Light Pulse Generator driver.

Signed-off-by: Luca Weiss <luca@z3ntu.xyz>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20230414-pmi632-v2-3-98bafa909c36@z3ntu.xyz