platform/x86: Kconfig: Remove unnecessary "if X86"

drivers/platform/x86/Kconfig is wrapped in one big
if X86_PLATFORM_DEVICES .. endif and X86_PLATFORM_DEVICES already
has a "depends on X86" so the "if X86" in drivers/platform/Kconfig
is not necessary and except for MIPS none of the other includes
there has such an if. So let's remove it.

While at it also move the x86/Kconfig include to the end of the file
for alphabetical sorting.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20220620145628.5882-2-hdegoede@redhat.com