platform/x86/dell: Kconfig: Remove unnecessary "depends on X86_PLATFORM_DEVICES"

platform/x86/dell/Kconfig is only sourced if X86_PLATFORM_DEVICES is set,
so it does not need to depend on it.

Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20220620145628.5882-3-hdegoede@redhat.com