drivers: display: st7735r: added inversion-on property

Add 'inversion-on' property to st7735r.
Issue INVON(21h) command on initializing if inversion-on was enabled.
As a result of this command, the display color is inverted.
Otherwise, INVOFF(20h) will be issued.

Signed-off-by: TOKITA Hiroshi <tokita.hiroshi@gmail.com>