toshiba_acpi: Unify hotkey enabling functions

Currently the driver has two functions enabling hotkeys support,
but these two functions can be merged into one.

This patch merges these two functions, moving some checks to the
*enable_hotkeys function, simplifying code in the process.

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