drm/msm/dsi: Add configuration for 28nm PLL on family B

The 28nm PLL has a different iospace on MSM/APQ family B SoCs:
add a new configuration and use it when the DT reports the
"qcom,dsi-phy-28nm-hpm-fam-b" compatible.

Signed-off-by: AngeloGioacchino Del Regno <kholk11@gmail.com>
Signed-off-by: Rob Clark <robdclark@chromium.org>