arm64: dts: n5x: drop invalid property and fix edac node name

The intel,sysmgr-syscon in EDAC/memory controller node is not a
recognized and documented property, so drop it to fix error:

  sdr_edac@f87f8000: 'intel,sysmgr-syscon' does not match any of the regexes: 'pinctrl-[0-9]+'

Align also the node name with Devicetree specification (generic, not
specific, and EDAC is purely Linux term).

Fixes: ef82c9be ("arm64: dts: n5x: add sdr edac support")
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20220318121044.108750-1-krzysztof.kozlowski@canonical.com

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Signed-off-by: Arnd Bergmann <arnd@arndb.de>