platform/x86: Add rfkill dependency to ACPI_TOSHIBA entry

Commit 2fdde834

 ("toshiba_acpi: Add WWAN RFKill support") added
WWAN rfkill support to the driver, but the KConfig entry was not
updated to add the RFKill dependency, causing a broken build if
RFKill is not selected.

This patch adds the RFKILL dependency to the KConfig entry, fixing
the build issue.

Signed-off-by: Azael Avalos <coproscefalo@gmail.com>
Signed-off-by: Darren Hart <dvhart@linux.intel.com>