drm/i915/dsb: Implement intel_dsb_gosub()

drm/i915/dsb: Implement intel_dsb_gosub()

Add support for the new GOSUB DSB instruction (available on ptl+),
which instructs the DSB to jump to a different buffer, execute
the commands there, and then return execution to the next
instruction in the original buffer.

There are a few alignment related workarounds that need to
be dealt with when emitting GOSUB instruction.

v2: Right shift head and tail pointer passed to gosub command (chaitanya)
v3: Add macro for right shifting head/tail pointers (Animesh)
v4: Fix typo in commit message (Uma)
    Add comments explaining why right shifting htp is needed (Animesh)

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Chaitanya Kumar Borah <chaitanya.kumar.borah@intel.com>
Reviewed-by: Uma Shankar <uma.shankar@intel.com>
Reviewed-by: Animesh Manna <animesh.manna@intel.com>
Signed-off-by: Animesh Manna <animesh.manna@intel.com>
Link: https://lore.kernel.org/r/20250523062041.166468-5-chaitanya.kumar.borah@intel.com