ARM: defconfig: turn off CONFIG_EXPERT

ARM: defconfig: turn off CONFIG_EXPERT

Since multi_v7_defconfig is meant to be the generic defconfig, many
users are not going to be experts and it is counterintuitive to have
CONFIG_EXPERT enabled.

This change has a couple of side-effects:

 - CONFIG_NAMESPACES is enabled by default. This adds about 0.2% of
  .text, but is already enabled in many board specific configs, and
   apparently a requirement for systemd, so this seems like a useful
   change.

 - CONFIG_DEBUG_MEMORY_INIT is enabled now, adding a tiny bit
   of code in the inittext section

 - CONFIG_RFKILL, CONFIG_MEDIA_SUPPORT_FILTER and various CONFIG_HID
   driver defaults change, so these have to be listed explicitly to
   maintain the previous behavior

 - CONFIG_SERIAL_SH_SCI_NR_UARTS=20 changes to the default value
   of 18, which I understand to be sufficient for any buard, even
   if all UARTS are enabled at the same time

Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20260112153255.795553-2-arnd@kernel.org
Signed-off-by: Arnd Bergmann <arnd@arndb.de>