arm64: defconfig: Enable additional support for Renesas platforms

Increase build and test coverage by enabling support for more hardware
present on Renesas SoCs and boards:
  - Renesas RSPI, RZ/G2L thermal, RZ/G2L WDT watchdog, and OSTM timer,
    as used on the RZ/G2L SMARC EVK board,
  - R-Car Image Signal Processor (ISP) and Display Unit embedded MIPI
    DSI encoder on R-Car V3U, as used on the Falcon board.

All of the above are modular, except for thermal, watchdog, and timer.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/c9800d67f91a90d418a3ce44c59109ae0a87b2d8.1643373223.git.geert+renesas@glider.be