drm/panel: nt35521: Break some CMDS into helper functions

Break select page cmds into helper functions.

Signed-off-by: Cong Yang <yangcong5@huaqin.corp-partner.google.com>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Link: https://lore.kernel.org/r/20240710084715.1119935-3-yangcong5@huaqin.corp-partner.google.com


Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240710084715.1119935-3-yangcong5@huaqin.corp-partner.google.com