arm64: Kconfig: provide a top-level switch for Microchip platforms

arm64: Kconfig: provide a top-level switch for Microchip platforms

Microchip is the only platform that doesn't have a top-level switch for
disabling all SoC families. Align it with other platforms and update the
arm64 defconfig to keep the default config the same.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>
Link: https://lore.kernel.org/r/20260226143615.65788-1-bartosz.golaszewski@oss.qualcomm.com
Signed-off-by: Claudiu Beznea <claudiu.beznea@tuxon.dev>