cec: backport 5.15 AOCEC driver to 4.9 with __ATTR table refactor

[samtheruby]

Backport changes

• Split monolithic hdmi_ao_cec.c into three files (hdmi_ao_cec.c, hdmi_aocec_api.c, hdmi_cec_dump.c) matching the 5.15 driver layout.
• Replace all aml_mbox calls with scpi_protocol equivalents:
  • MBOX_CMD_SET_CEC_DATA -> scpi_send_cec_data / scpi_send_usr_data
  • MBOX_CMD_GET_CEC1/2 -> scpi_get_cec_val
  • MBOX_CMD_GET_CEC_OTP/AS_MSG -> scpi_get_cec_wk_msg
• Add get_hdmitx_phy_addr() shim (5.15 accessor not in 4.9 hdmi_tx_ext.h).
• CEC_MAIL_BOX and CEC_FREEZE_WAKE_UP intentionally left undefined: 4.9 uses scpi_protocol; freeze/s2idle not supported on ng hardware.
• HPD regression fix: 5.15 cec_hdmi_plug_handler clears stale phy_addr on unplug, preventing phantom active-source responses.
• Add null guards to hdmitx/hdmirx notify callbacks against races during driver probe/remove.
• Drop CONFIG_AMLOGIC_HDMITX21 guards (not in 4.9); fix CONFIG_HAS_EARLYSUSPEND -> CONFIG_AMLOGIC_LEGACY_EARLY_SUSPEND; fix HDMIRX include path for 4.9 tree layout.
• Remove the missing linux/earlysuspend.h include — all needed declarations come from linux/amlogic/pm.h under CONFIG_AMLOGIC_LEGACY_EARLY_SUSPEND.

Refactor on top

• Replace per-attribute CLASS_ATTR_xx static declarations and the aocec_class_attrs[] pointer array with a single aocec_class_attr_list[] table built from __ATTR_xx macros. Same set of attributes, same RW/RO/WO semantics; cleans up the namespace and makes adding new attributes a one-line change.

Test plan

• Build + flash on G12B/S922Z.
• Confirm `/sys/class/aocec/*` exposes the expected attribute set with correct R/W permissions.
• CEC enumeration with a TV: logical address claim, polling, vendor ID exchange.
• Route change: switch active source between Kodi and another HDMI input; verify the device releases / re-claims correctly.
• Power round-trip: TV power-on/off, standby, wake-up — verify ACTIVE_SOURCE and IMAGE_VIEW_ON behave.
• HPD plug/unplug while running: previous regression (stale phy_addr after unplug) should be gone.
• Regression test on SM1 (S905X3) if available.
• libCEC interop with Kodi's PeripheralCecAdapter end-to-end.

[samtheruby]

All possible tests passed, As well as 0 bugs when in regular use, I think this is ready for prime time!

[samtheruby]

Please note this also requires the fix pannal/CoreELEC#52