arm64: dts: renesas: r8a779a0: Correct avb[01] reg sizes

All Ethernet AVB instances on R-Car V3U have registers related to UDP/IP
support, but the declared register blocks for the first two instances
are too small to cover them.

Fix this by extending the register block sizes.

Fixes: 5a633320 ("arm64: dts: renesas: r8a779a0: Add Ethernet-AVB support")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/ce6ce3c4b1495e02e7c1803fca810a7178a84500.1707660323.git.geert+renesas@glider.be