drm/radeon: remove load callback from kms_driver

[Arthur Marsh]

Recent kernels resulted in a blank screen, with Xorg.0.log reporting:

(II) [KMS] drm report modesetting isn't supported.

Sometimes while bisecting the pc came to a complete lockup (magic Sysreq 
unresponsive).

At the end of bisecting I had:

90985660ba488cd3428706e7d53d6c9cdbbf3101 is the first bad commit
commit 90985660ba488cd3428706e7d53d6c9cdbbf3101
Author: Wu Hoi Pok <wuhoipok at gmail.com>
Date:   Sun Jun 30 12:59:18 2024 -0400

    drm/radeon: remove load callback from kms_driver
    
    The ".load" callback in "struct drm_driver" is deprecated. In order to remove
    the callback, we have to manually call "radeon_driver_load_kms" instead.

This machine reports having:

AMD A10-6800K APU with Radeon HD Graphics

with the gpu appearing as 

Advanced Micro Devices [AMD/ATI] Richland [Radeon HD 8670D] 1002:990c

Regards,

Arthur Marsh.