dell-wmi, dell-laptop: depends DMI

dell-wmi and dell-laptop will compile but won't work right if DMI
isn't selected.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Acked-by: Pali Rohár <pali.rohar@gmail.com>

[arnd: Use depends instead of selects to avoid recursive dependencies]

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Darren Hart <dvhart@linux.intel.com>