drivers/tty/vt/vt_ioctl.c: Include <linux/suspend.h> for pm_set_vt_switch

C files should include the header files that prototype their functions.
This keeps the types in sync, and eliminates warnings from GCC
(-Wmissing-prototypes) and Sparse (-Wdecl).

Signed-off-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>