drm/i915/gt: Move SFC lock bits to intel_engine_regs.h

These SFC registers were defined in an unusual way, taking an engine as
a parameter rather than an engine MMIO base offset.  Let's adjust them
to match the style used by other per-engine registers and move them to
intel_engine_regs.h.

While doing this move, we can drop GEN12_HCP_SFC_FORCED_LOCK completely;
it was intended for use in an early version of a hardware workaround,
but was no longer necessary by the time the workaround was finalized.
It is not used anywhere in the driver.

Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Matt Atwood <matthew.s.atwood@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220209051140.1599643-3-matthew.d.roper@intel.com