drm/i915: Revert relocation chaining commits.

drm/i915: Revert relocation chaining commits.

This reverts commit f57e6886513f1 ("drm/i915/gem: Use chained reloc batches")
and commit 4c2bd46ee7c23 ("drm/i915/gem: Use a single chained reloc batches
for a single execbuf").

When adding ww locking to execbuf, it's hard enough to deal with a
single BO that is part of relocation execution. Chaining is hard to
get right, and with GPU relocation deprecated, it's best to drop this
altogether, instead of trying to fix something we will remove.

This is not a completely 1:1 revert, we reset rq_size to 0 in
reloc_cache_init, this was from cffc34ada3bc ("drm/i915/gem: Implement legacy
MI_STORE_DATA_IMM"), because we don't want to break the selftests. (Daniel)

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20200819140904.1708856-3-maarten.lankhorst@linux.intel.com
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>