drm/xe/gsc: Handle GSCCS ER interrupt

Starting on Xe2, the GSCCS engine reset is a 2-step process. When the
driver or the GuC hits the GDRST register, the CS is immediately reset
and a success is reported, but the GSC shim continues its reset in the
background. While the shim reset is ongoing, the CS is able to accept
new context submission, but any commands that require the shim will
be stalled until the reset is completed. This means that we can keep
submitting to the GSCCS as long as we make sure that the preemption
timeout is big enough to cover any delay introduced by the reset; since
the GSC preempt timeout is not tunable at runtime, we only need to check
that the value set in kconfig is big enough (and increase it if it
isn't).
When the shim reset completes, a specific CS interrupt is triggered,
in response to which we need to check the GSCI_TIMER_STATUS register
to see if the reset was successful or not.
Note that the GSCI_TIMER_STATUS register is not power save/restored,
so it gets reset on MC6 entry. However, a reset failure stops MC6,
so in that scenario we're always guaranteed to find the correct value.

Since we can't check the register within interrupt context, the
existing GSC worker has been updated to handle it.
The expected action to take on ER failure is to trigger a driver FLR,
but we still don't support that, so for now we just print an error. A
comment has been added to the code to keep track of the FLR requirement.

v2: Add a check for the initial timeout value (Alan)

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Alan Previn <alan.previn.teres.alexis@intel.com>
Reviewed-by: Alan Previn <alan.previn.teres.alexis@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240304145634.820684-1-daniele.ceraolospurio@intel.com

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