arm64: dts: qcom: msm8998-xperia: Configure display boost regulators

Add configuration for the LAB and IBB regulators (in boost mode):
this platform has smartphones with three different display sizes,
hence different displays requiring different voltage.

The common configuration parameters have been put in the common
device-tree, while specific voltage specs and soft-start-us are
variant specific, so they have been put into the machine specific
dts file.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@somainline.org>
Reviewed-by: Marijn Suijten <marijn.suijten@somainline.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20210909123733.367248-5-angelogioacchino.delregno@somainline.org