The syscon nodes should come with specific compatible.  Correct the
FSYS syscon to fix dtbs_check warnings:

  syscon@156f0000: compatible: 'anyOf' conditional failed, one must be fixed:
  ['syscon'] is too short
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Reviewed-by: Alim Akhtar <alim.akhtar@samsung.com>
Link: https://lore.kernel.org/r/20210820082149.84613-1-krzysztof.kozlowski@canonical.com