drivers: display: st7735r: Add rgb-is-inverted property

Set the inverted value of pixel format setting in MADCTL register to
current_pixel_format in display capabilities structure
if rgb-is-inverted enabled.

This make enables support for a module that mismatches the RGB setting
in the MADCTL register and the actual display color format.
(Such as Longan Nano built-in LCD module.)

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