pinctrl: renesas: r8a779g0: Fix FXR_TXEN[AB] suffixes

The Pin Multiplex attachment in Rev.1.10 of the R-Car V4H Series
Hardware User's Manual still has two alternate pins named both
"FXR_TXEN[AB]".  To differentiate, the pin control driver uses
"FXR_TXEN[AB]" and "FXR_TXEN[AB]_X", which were considered temporary
names until the conflict was sorted out.

Fix this by adopting R-Car V4M naming:
  - Rename "FXR_TXEN[AB]" to "FXR_TXEN[AB]_A",
  - Rename "FXR_TXEN[AB]_X" to "FXR_TXEN[AB]_B".

Fixes: ad9bb2fe ("pinctrl: renesas: Initial R8A779G0 (R-Car V4H) PFC support")
Fixes: 1c2646b5 ("pinctrl: renesas: r8a779g0: Add missing FlexRay")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/5e1e9abb46c311d4c54450d991072d6d0e66f14c.1717754960.git.geert+renesas@glider.be