drivers: display: display_hx8394: use MIPI LPM during init commands

Although not documented in the HX8394 datasheet, it seems that the
display fails to initialize if MIPI HS mode is used to send
configuration commands. Therefore, we must make sure all initialization
commands are sent with the MIPI_DSI_MSG_USE_LPM flag set.

Signed-off-by: Daniel DeGrasse <daniel.degrasse@nxp.com>