arm64: dts: renesas: r9a09g047: Enable Tx coe support

arm64: dts: renesas: r9a09g047: Enable Tx coe support

The GBETH IPs found on RZ/G3E SoC family are compatible with the stmmac
driver.  They have a MAC HW feature register used by this driver to
enable respective features.  While the register advertises Tx coe
support, it was not enabled by the driver due to the
'snps,force_thresh_dma_mode' dtsi property.

Switch from 'snps,force_thresh_dma_mode' to 'snps,force_sf_dma_mode' to
enable Tx checksum offload support on both GBETH IPs.  While at it, also
switch from 'snps,fixed-burst' to 'snps,mixed-burst' and remove
'snps,no-pbl-x8' for optimal DMA configuration.  This improvement
results in a measurable TCP Tx performance gain, increasing throughput
by 20Mbps.

Signed-off-by: John Madieu <john.madieu.xa@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://patch.msgid.link/20250814153456.268208-1-john.madieu.xa@bp.renesas.com
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>