drm: support routines for HDMI/DP ELD

ELD (EDID-Like Data) describes to the HDMI/DP audio driver the audio
capabilities of the plugged monitor.

This adds drm_edid_to_eld() for converting EDID to ELD. The converted
ELD will be saved in a new drm_connector.eld[128] data field. This is
necessary because the graphics driver will need to fixup some of the
data fields (eg. HDMI/DP connection type, AV sync delay) before writing
to the hardware ELD buffer. drm_av_sync_delay() will help the graphics
drivers dynamically compute the AV sync delay for fixing-up the ELD.

ELD selection policy: it's possible for one encoder to be associated
with multiple connectors (ie. monitors), in which case the first found
ELD will be returned by drm_select_eld(). This policy may not be
suitable for all users, but let's start it simple first.

The impact of ELD selection policy: assume there are two monitors, one
supports stereo playback and the other has 8-channel output; cloned
display mode is used, so that the two monitors are associated with the
same internal encoder. If only the stereo playback capability is reported,
the user won't be able to start 8-channel playback; if the 8-channel ELD
is reported, then user space applications may send 8-channel samples
down, however the user may actually be listening to the 2-channel
monitor and not connecting speakers to the 8-channel monitor.

According to James, many TVs will either refuse the display anything or
pop-up an OSD warning whenever they receive hdmi audio which they cannot
handle. Eventually we will require configurability and/or per-monitor
audio control even when the video is cloned.

CC: Zhao Yakui <yakui.zhao@intel.com>
CC: Wang Zhenyu <zhenyu.z.wang@intel.com>
CC: Jeremy Bush <contractfrombelow@gmail.com>
CC: Christopher White <c.white@pulseforce.com>
CC: Pierre-Louis Bossart <pierre-louis.bossart@intel.com>
CC: Paul Menzel <paulepanter@users.sourceforge.net>
CC: James Cloos <cloos@jhcloos.com>
CC: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Keith Packard <keithp@keithp.com>
drm/i915: pass ELD to HDMI/DP audio driver

Add ELD support for Intel Eaglelake, IbexPeak/Ironlake,
SandyBridge/CougarPoint and IvyBridge/PantherPoint chips.

ELD (EDID-Like Data) describes to the HDMI/DP audio driver the audio
capabilities of the plugged monitor. It's built and passed to audio
driver in 2 steps:

(1) at get_modes time, parse EDID and save ELD to drm_connector.eld[]

(2) at mode_set time, write drm_connector.eld[] to the Transcoder's hw
    ELD buffer and set the ELD_valid bit to inform HDMI/DP audio driver

This patch is tested OK on G45/HDMI, IbexPeak/HDMI and IvyBridge/HDMI+DP.
Test scheme: plug in the HDMI/DP monitor, and run

        cat /proc/asound/card0/eld*

to check if the monitor name, HDMI/DP type, etc. show up correctly.

Minor imperfection: the GEN5_AUD_CNTL_ST/DIP_Port_Select field always
reads 0 (reserved). Without knowing the port number, I worked it around
by setting the ELD_valid bit for ALL the three ports. It's tested to not
be a problem, because the audio driver will find invalid ELD data and
hence rightfully abort, even when it sees the ELD_valid indicator.

Thanks to Zhenyu and Pierre-Louis for a lot of valuable help and testing.

CC: Zhao Yakui <yakui.zhao@intel.com>
CC: Wang Zhenyu <zhenyu.z.wang@intel.com>
CC: Jeremy Bush <contractfrombelow@gmail.com>
CC: Christopher White <c.white@pulseforce.com>
CC: Pierre-Louis Bossart <pierre-louis.bossart@intel.com>
CC: Paul Menzel <paulepanter@users.sourceforge.net>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Keith Packard <keithp@keithp.com>
New defconfig with cpufreq defaulting to ondemand and with dummy alsa device.