drm/i915: Kill GEN_FOREVER

commit ac657f64 ("drm/i915: Introduce IS_GEN macro") introduced
GEN_FOREVER that was never used.

My first attempt was to rename it to FOREVER since GEN is
already part of the macro. Then I used coccinelle to change all
-INTEL_GEN(e1) >= e2
+INTEL_GEN_RANGE(e1, e2, FOREVER)
-INTEL_GEN(e1) <= e2
+INTEL_GEN_RANGE(e1, 0, e2)

and I liked it.

However I didn't like very much the remaining
INTEL_GEN(dev_priv) < n

and:
INTEL_GEN(e1) < n
INTEL_GEN_RANGE(e1, 0, n - 1)

didn't make much sense either.

So INTEL_GEN use for > or < seems a better unified way for unlimited
bounds. So, no reason to keep GEN_FOREVER here.

Let's kill before someone start using it.

v2: Remove remaining GEN_FOREVER forgotten in a comment. (Daniel)

Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20181026195143.20353-2-rodrigo.vivi@intel.com