ARM: shmobile: defconfig: Refresh for v5.19-rc1

Refresh the defconfig for Renesas ARM systems:
  - Move CONFIG_SLAB=y (moved in commit 7b42f104 ("mm: Kconfig:
    move swap and slab config options to the MM section")),
  - Enable CONFIG_RENESAS_RZN1WDT (RZN1D-DB),
  - Enable CONFIG_RTC_DRV_RZN1 (RZN1-DB).

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/7ef31a41e1a15d0cedeb6cfc496ce70a78102e32.1654855000.git.geert+renesas@glider.be