package/mesa3d: drop r100 dependency on _HAS_ATOMIC

package/mesa3d: drop r100 dependency on _HAS_ATOMIC

This partially reverts commit a3aac6d84713db7e6d2683eabf965eae21ce48bf,
just dropping the atomic dependency.

That dependency would introduce a "recursive dependency" chain in
Kconfig.

However, r100 is only available on i386 and x86-64, and they both have
sync4, which means libdrm's HAS_ATOMICS is always 'y' when r100 is
available.

So, like we did in 00c1a8c34f7 (package/mesa3d: propagate missing
libdrm-freedreno deps), we just add a fat comment that explains why the
dependency is not propagated.

Reported-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Cc: James Hilliard <james.hilliard1@gmail.com>
Cc: Bernd Kuhls <bernd.kuhls@t-online.de>