Add pmic-gpio compatible string for pmm8155au pmic
found on the SA8155p-adp board.

Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Bjorn Andersson <bjorn.andersson@linaro.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Bhupesh Sharma <bhupesh.sharma@linaro.org>
Link: https://lore.kernel.org/r/20210629123407.82561-3-bhupesh.sharma@linaro.orgSigned-off-by: Linus Walleij <linus.walleij@linaro.org>