drm/st7571-i2c: select CONFIG_DRM_CLIENT_SELECTION

drm/st7571-i2c: select CONFIG_DRM_CLIENT_SELECTION

The newly added driver calls drm_client_setup(), but that is not
always built in:

x86_64-linux-ld: vmlinux.o: in function `st7571_probe':
st7571-i2c.c:(.text+0x7b7119): undefined reference to `drm_client_setup'

Select the appropriate Kconfig symbol.

Fixes: 4b35f0f41ee2 ("drm/st7571-i2c: add support for Sitronix ST7571 LCD controller")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Marcus Folkesson <marcus.folkesson@gmail.com>
Link: https://lore.kernel.org/r/20250428150752.3970145-1-arnd@kernel.org
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>