ARM: shmobile: defconfig: Refresh for v5.12-rc2

Refresh the defconfig for Renesas ARM systems:
  - Drop CONFIG_ENABLE_MUST_CHECK=n (removed in commit 19679394
    ("Compiler Attributes: remove CONFIG_ENABLE_MUST_CHECK")).
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20210310103213.2529983-1-geert+renesas@glider.be

arch/arm/configs/shmobile_defconfig

@@ -220,6 +220,5 @@ CONFIG_NLS_ISO8859_1=y
 CONFIG_DMA_CMA=y
 CONFIG_CMA_SIZE_MBYTES=64
 CONFIG_PRINTK_TIME=y
-# CONFIG_ENABLE_MUST_CHECK is not set
 CONFIG_DEBUG_FS=y
 CONFIG_DEBUG_KERNEL=y