arm64: dts: agilex: align mmc node names with dtschema

The Synopsys DW MSHC bindings require node name to be 'mmc':

  dwmmc0@ff808000: $nodename:0: 'dwmmc0@ff808000' does not match '^mmc(@.*)?$'

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>