arm64: dts: allwinner: a523: Rename emac0 to gmac0

arm64: dts: allwinner: a523: Rename emac0 to gmac0

The datasheets refer to the first Ethernet controller as GMAC0, not
EMAC0.

Fix the compatible string, node label and pinmux function name to match
what the datasheets use. A change to the device tree binding is sent
separately.

Fixes: 56766ca6c4f6 ("arm64: dts: allwinner: a523: Add EMAC0 ethernet MAC")
Fixes: acca163f3f51 ("arm64: dts: allwinner: a527: add EMAC0 to Radxa A5E board")
Fixes: c6800f15998b ("arm64: dts: allwinner: t527: add EMAC0 to Avaota-A1 board")
Link: https://patch.msgid.link/20250628054438.2864220-3-wens@kernel.org
Signed-off-by: Chen-Yu Tsai <wens@csie.org>