arm64: dts: qcom: x1e78100-t14s: mark l12b and l15b always-on

arm64: dts: qcom: x1e78100-t14s: mark l12b and l15b always-on

The l12b and l15b supplies are used by components that are not (fully)
described (and some never will be) and must never be disabled.

Mark the regulators as always-on to prevent them from being disabled,
for example, when consumers probe defer or suspend.

Fixes: 7d1cbe2f4985 ("arm64: dts: qcom: Add X1E78100 ThinkPad T14s Gen 6")
Cc: stable@vger.kernel.org	# 6.12
Reviewed-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Link: https://lore.kernel.org/r/20250314145440.11371-3-johan+linaro@kernel.org
Signed-off-by: Bjorn Andersson <andersson@kernel.org>