drm: add separate drm debugging levels

Now all the DRM debug info will be reported if the boot option of
"drm.debug=1" is added. Sometimes it is inconvenient to get the debug
info in KMS mode. We will get too much unrelated info.

This will separate several DRM debug levels and the debug level can be used
to print the different debug info. And the debug level is controlled by the
module parameter of drm.debug

In this patch it is divided into four debug levels;
       	drm_core, drm_driver, drm_kms, drm_mode.

At the same time we can get the different debug info by changing the debug
level. This can be done by adding the module parameter. Of course it can
be changed through the /sys/module/drm/parameters/debug after the system is
booted.

Four debug macro definitions are provided.
	DRM_DEBUG(fmt, args...)
	DRM_DEBUG_DRIVER(prefix, fmt, args...)
	DRM_DEBUG_KMS(prefix, fmt, args...)
	DRM_DEBUG_MODE(prefix, fmt, args...)

When the boot option of "drm.debug=4" is added, it will print the debug info
using DRM_DEBUG_KMS macro definition.
When the boot option of "drm.debug=6" is added, it will print the debug info
using DRM_DEBUG_KMS/DRM_DEBUG_DRIVER.

Sometimes we expect to print the value of an array.
For example: SDVO command,
In such case the following four DRM debug macro definitions are added:
	DRM_LOG(fmt, args...)
	DRM_LOG_DRIVER(fmt, args...)
	DRM_LOG_KMS(fmt, args...)
	DRM_LOG_MODE(fmt, args...)

Signed-off-by: Zhao Yakui <yakui.zhao@intel.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>