package/mesa3d: fix circular dependency in Kconfig

package/mesa3d: fix circular dependency in Kconfig

When the r300 driver was introduced in c5ae77c97 (package/mesa3d: add
support for gallium r300 driver), a last-minute fix was introduced by
Yann, to properly propagate the dependency of a selected symbol.

However, this ended up causing a spurious circular dependency that does
not really exists, but that Kconfig is not smart enough to detect is in
fact OK.

Fixing this is pretty non-obvious, but we have an easy way out: the
dependency is about libdrm's radeon driver requirement for a toolchain
that has the sync4 family of primitives, which is always a given for an
x86 toolchain. As the radeon r300 driver is x86-only, this dependency is
forcefully fulfilled.

So, we drop the propagated dependency, and replace it by a fat comment.

Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Cc: Romain Naour <romain.naour@gmail.com>
Cc: Bernd Kuhls <bernd.kuhls@t-online.de>
Cc: James Hilliard <james.hilliard1@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>