arm64: dts: exynos: gs101: add reboot-mode support (SYSIP_DAT0)

arm64: dts: exynos: gs101: add reboot-mode support (SYSIP_DAT0)

syscon-reboot-mode can be used to indicate the reboot mode for the
bootloader.

While not sufficient for all boot modes, the boot loader does use
SYSIP_DAT0 (PMU + 0x0810) to determine some of the actions it should
take. This change helps it deciding what to do in those cases.

For complete support, we'll also have to write the boot mode to an
NVMEM storage location, but we have no upstream driver for that yet.
Nevertheless, this patch is a step towards full support for the boot
mode.

Note1: Android also uses 'shutdown,thermal' and
shutdown,thermal,battery', but that can not be described in DT as ','
is used to denote vendor prefixes. I've left them out from here for
that reason.

Note2: downstream / bootloader recognizes one more mode: 'dm-verity
device corrupted' with value 0x50, but we can not describe that in DT
using a property name due to the space, so it's been left out from here
as well. This string appears to come from drivers/md/dm-verity-target.c
and should probably be changed there in a follow-up patch, so that it
can be used in reboot-mode nodes like this one here.

Reviewed-by: Peter Griffin <peter.griffin@linaro.org>
Signed-off-by: André Draszik <andre.draszik@linaro.org>
Link: https://lore.kernel.org/r/20250210-gs101-renppt-dts-v2-3-fb33fda6fc4b@linaro.org
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>