drm/i915: Keep the ctx workarounds tightly packed

For each platform, we have a few registers that are rewritten with
different values -- they are not part of a sequence, just different parts
of a masked register set at different times (e.g. platform and gen
workarounds). Consolidate these into a single register write to keep the
table compact, important since we are running of room in the current
fixed sized buffer.

While adjusting the construction of the wa table, make it non fatal so
that the driver still loads but keeping the warning and extra details
for inspection.

Inspecting the changes for a Kabylake system,
Before:
	Address	val		mask		read
	0x07014	0x20002000	0x00002000	0x00002100
	0x0E194	0x01000100	0x00000100	0x00000114
	0x0E4F0	0x81008100	0x00008100	0xFFFF8120
	0x0E184	0x00200020	0x00000020	0x00000022
	0x0E194	0x00140014	0x00000014	0x00000114
	0x07004	0x00420042	0x00000042	0x000029C2
	0x0E188	0x00080000	0x00000008	0x00008030
	0x07300	0x80208020	0x00008020	0x00008830
	0x07300	0x00100010	0x00000010	0x00008830
	0x0E184	0x00020002	0x00000002	0x00000022
	0x0E180	0x20002000	0x00002000	0x00002000
	0x02580	0x00010000	0x00000001	0x00000004
	0x02580	0x00060004	0x00000006	0x00000004
	0x07014	0x01000100	0x00000100	0x00002100
	0x0E100	0x00100010	0x00000010	0x00008050

After:
	Address	val		mask		read
	0x02580	0x00070004	0x00000007	0x00000004
	0x07004	0x00420042	0x00000042	0x000029C2
	0x07014	0x21002100	0x00002100	0x00002100
	0x07300	0x80308030	0x00008030	0x00008830
	0x0E100	0x00100010	0x00000010	0x00008050
	0x0E180	0x20002000	0x00002000	0x00002000
	0x0E184	0x00220022	0x00000022	0x00000022
	0x0E188	0x00080000	0x00000008	0x00008030
	0x0E194	0x01140114	0x00000114	0x00000114
	0x0E4F0	0x81008100	0x00008100	0xFFFF8120

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Oscar Mateo <oscar.mateo@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180615120207.13952-1-chris@chris-wilson.co.uk