arm64: dts: bitmain: Modify pin controller memory map

Earlier, the PWM registers were included as part of the pinctrl memory
map, but this turned to be useless as the muxing is being handled by the
SoC pin controller itself. Hence, this commit removes the pwm register
mapping from the pinctrl node to make it more clean.

Fixes: af2ff87de413 ("arm64: dts: bitmain: Add pinctrl support for BM1880 SoC")
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>