ttm_bo_list_ref_sub(): Compare old value to "count" before release list

For instance, "count" can be 0 and if "old" is 1, the list must not be
released.
TTM: kref_init() on Linux set the initial ref to 1, not 0
Use DRM_LOCK(dev) instead of sx_xlock(&dev->dev_struct_lock)
radeon_irq_kms_init(): Unlock drm_device before calling drm_irq_install()
radeon: Enable I2C bus setup
radeon_i2c.c: Look for iicbus among iicbb's children

... not radeon_iicbb's.
radeon: Set radeon_*_i2c's softc in radeon_i2c_create()
radeon: Normalize firmware names
ttm: Fix arguments to vm_page_alloc_config()

- flags |= VM_ALLOC_NOOBJ
- max address = VM_MAX_ADDRESS
- alignment = PAGE_SIZE
radeon: Implement dummy_page using a drm_dma_handle_t
radeon_fbdev_destroy: Unlock drm_device before calling radeonfb_destroy_pinned_object

This fixes a panic caused by a recursed lock of the drm_device
structure.