msi-laptop: fix config-dependent build error

The msi-laptop driver uses input_*() and sparse_keymap_*() interfaces.
It should depend on the INPUT subsystem being present and select
INPUT_SPARSEKMAP so that those interfaces are present.

ERROR: "input_free_device" [drivers/platform/x86/msi-laptop.ko] undefined!
ERROR: "input_register_device" [drivers/platform/x86/msi-laptop.ko] undefined!
ERROR: "sparse_keymap_setup" [drivers/platform/x86/msi-laptop.ko] undefined!
ERROR: "input_allocate_device" [drivers/platform/x86/msi-laptop.ko] undefined!
ERROR: "sparse_keymap_report_event" [drivers/platform/x86/msi-laptop.ko] undefined!
ERROR: "input_unregister_device" [drivers/platform/x86/msi-laptop.ko] undefined!
ERROR: "sparse_keymap_free" [drivers/platform/x86/msi-laptop.ko] undefined!

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Matthew Garrett <mjg@redhat.com>
Cc: "Lee, Chun-Yi" <jlee@novell.com>
Signed-off-by: Matthew Garrett <mjg@redhat.com>