drm/panel: st7703: Rename functions from jh057n prefix to st7703

This is done so that code that's not specific to a particular
jh057n panel is named after the controller. Functions specific
to the panel are kept named after the panel.

Signed-off-by: Ondrej Jirman <megous@megous.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Tested-by: Guido Günther <agx@sigxcpu.org>
Reviewed-by: Guido Günther <agx@sigxcpu.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200701162928.1638874-6-megous@megous.com