Documentation/process: maintainer-soc: document dtbs_check requirement for Samsung

Samsung ARM/ARM64 SoCs (except legacy S5PV210) are also expected not to
bring any new dtbs_check warnings. In fact this have been already
enforced and tested since few release.

Cc: Conor Dooley <[e-mail]>
Signed-off-by: Krzysztof Kozlowski <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Arnd Bergmann <[e-mail]>

Documentation/process/maintainer-soc.rst

···
 more information on the validation of devicetrees.
 
 For new platforms, or additions to existing ones, ``make dtbs_check`` should not
-add any new warnings.  For RISC-V, as it has the advantage of being a newer
-architecture, ``make dtbs_check W=1`` is required to not add any new warnings.
+add any new warnings.  For RISC-V and Samsung SoC, ``make dtbs_check W=1`` is
+required to not add any new warnings.
 If in any doubt about a devicetree change, reach out to the devicetree
 maintainers.