drm/i915/dp: Read/ack sink count and sink IRQs for SST as it's done for MST

drm/i915/dp: Read/ack sink count and sink IRQs for SST as it's done for MST

Read and ack the sink count, sink device and link service IRQs for SST
the same way this is done for MST, the read/ack happening in separate
steps via an ESI (Event Status Indicator) vector.

The above way is more efficient, since on newer (DPCD_REV >= 1.2) sinks
the DP_SINK_COUNT_ESI..DP_LINK_SERVICE_IRQ_VECTOR_ESI0 registers can be
read out in one AUX transaction - and the 3 last one written in one
transaction. Also this allows sharing more of the SST and MST IRQ
handling code (done as a follow-up).

For now keep the current behavior of always reading the legacy
DP_SINK_COUNT, DP_DEVICE_SERVICE_IRQ_VECTOR registers and not reading
the DP_DEVICE_SERVICE_IRQ_VECTOR_ESI1 register.

v2: Document the ESI vector get/ack helper fnuctions' return value.
    (Jani, Luca)

Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Luca Coelho <luciano.coelho@intel.com>
Reviewed-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patch.msgid.link/20260225164618.1261368-16-imre.deak@intel.com