drm/stm: drv: Rename platform driver name

drm/stm: drv: Rename platform driver name

Rename the platform driver name from "stm" to "stm32-display"
for a better readability in /sys/bus/platform/drivers entries.

Note: We keep "stm" as drm_driver.name because it is better
when using "modetest -M stm ..." (even if recent modetest patch
avoids using -M).

Signed-off-by: Philippe CORNU <philippe.cornu@st.com>
Reviewed-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Signed-off-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/1500552357-29487-2-git-send-email-philippe.cornu@st.com