dma-buf: Documentation update for Kconfig select
dma-buf: Documentation update for Kconfig select

As per Linus' comment, dma-buf Kconfig entry shouldn't have an option
text, but should be selected by the subsystems that use it.

Add this information in the documentation as well.

Signed-off-by: Sumit Semwal <d6930da0d649c01d063dcca4d796c2ac2cbb68ba@ti.com>
Signed-off-by: Dave Airlie <f2295d84e358395675bc8031be58672073ae065e@redhat.com>

KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs