drm/amdgpu: add EDC support for CZ (v3)

BugLink: http://bugs.launchpad.net/bugs/1546572

This adds EDC support for CZ.
EDC = Error Correction and Detection
This code properly initializes the EDC hardware and
resets the error counts.  This is done in late_init
since it requires the IB pool which is not initialized
during hw_init.

v2: fix the IB size as noted by Felix, fix shader pgm
register programming
v3: use the IB for the shaders as suggested by Christian
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit ccba7691)
Signed-off-by: Alberto Milone <alberto.milone@canonical.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>