drm: select DRM_KMS_HELPER from DRM_GEM_SHMEM_HELPER

In the combination of DRM_KMS_HELPER=m, DRM_GEM_SHMEM_HELPER=y, DRM_FBDEV_EMULATION=y,
The shmem code fails to link against the KMS helpers:

x86_64-linux-ld: vmlinux.o: in function `drm_fbdev_shmem_driver_fbdev_probe':
(.text+0xeec601): undefined reference to `drm_fb_helper_alloc_info'
x86_64-linux-ld: (.text+0xeec633): undefined reference to `drm_fb_helper_fill_info'
x86_64-linux-ld: vmlinux.o: in function `drm_fbdev_shmem_get_page':
drm_fbdev_shmem.c:(.text+0xeec7d2): undefined reference to `drm_gem_fb_get_obj'
x86_64-linux-ld: vmlinux.o: in function `drm_fbdev_shmem_fb_mmap':
drm_fbdev_shmem.c:(.text+0xeec9f6): undefined reference to `drm_gem_fb_get_obj'
x86_64-linux-ld: vmlinux.o: in function `drm_fbdev_shmem_defio_imageblit':
(.rodata+0x5b2288): undefined reference to `drm_fb_helper_check_var'
x86_64-linux-ld: (.rodata+0x5b2290): undefined reference to `drm_fb_helper_set_par'

This can happen for a number of device drivers that select DRM_GEM_SHMEM_HELPER
without also selecting DRM_KMS_HELPER. To work around this, add another select
that forces DRM_KMS_HELPER to be built-in rather than a loadable module, but
only if FBDEV emulation is also enabled. DRM_TTM_HELPER and DRM_GEM_DMA_HELPER
look like they have the same problem in theory even if there is no possible
configuration that shows it. For consistency, do the same change to those.

Closes: https://lore.kernel.org/all/20250121-greedy-flounder-of-abundance-4d2ee8-mkl@pengutronix.de


Reported-by: Marc Kleine-Budde <mkl@pengutronix.de>
Tested-by: Marc Kleine-Budde <mkl@pengutronix.de>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20250122090211.3161186-1-arnd@kernel.org