Keymaps used by drivers based on matrix-keymap facilities are arrays of
unsigned shorts, not chars. Treating them otherwise produces corrupted
keymaps.

Reported-by: Sourav Poddar <sourav.poddar@ti.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

When platform keymap is not supplied to matrix_keypad_build_keymap()
and device tree support is enabled, try locating specified property
and load keymap from it. If property name is not defined, try using
"linux,keymap".

Based on earlier patch by Viresh Kumar <viresh.kumar@st.com>

Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

Change matrix-keymap helper to be out-of-line, like sparse keymap,
allow the helper perform basic keymap validation and return errors,
and prepare for device tree support.

Signed-off-by: Dmitry Torokhov <dtor@mail.ru>