Revert "x11-drivers/xf86-video-ati: port to EAPI 7"

Revert "x11-drivers/xf86-video-ati: port to EAPI 7"

In the port to EAPI=7, we stopped inheriting xorg-2 since that eclass is
not EAPI 7 ready. Unfortunately it was providing some critical
functionality:

[[ ${PN} == xf86-video-* || ${PN} == xf86-input-* ]] && DRIVER="yes"
...
xorg-2_flags_setup() {
...
    [[ ${PN} = xorg-server || -n ${DRIVER} ]] && append-ldflags -Wl,-z,lazy

In order to revert this commit, we must revert some commits that fix
problems introduced by it as well. In total:

This reverts commit f81770e41df51ad850fa78d6f57d7972a9e536bf.

Revert "x11-drivers/xf86-video-ati: Fix QA syntax errors"

This reverts commit 3339c825251a9809d573a98b94f36befe3286de9.

Revert "x11-drivers/xf86-video-ati: fix xorg-server:= dependency"

This reverts commit 6d94f4276b3cc284014af3177e0bc35168315b30.

Revert "x11-drivers/xf86-video-ati: add --disable-selective-werror"

This reverts commit 3313b2661bef1e56f0d089cc5b2c6f2d470fb6be.

Closes: https://bugs.gentoo.org/661562