This patch replaces kzalloc's flag from GFP_KERNEL to
GFP_ATOMIC to avoid sleeping in atomic context.

Below is the stack trace:

BUG: sleeping function called from invalid context at mm/slab.h:***
in_atomic(): 1, irqs_disabled(): 0, pid: 1137, name: DrmThread
CPU: 1 PID: 1137 Comm: DrmThread Tainted: G        W       4.14.43 #10
Call Trace:
 dump_stack+0x4d/0x63
 ___might_sleep+0x11f/0x12e
 __kmalloc+0x76/0x126
 amdgpu_atom_execute_table_locked+0xfc/0x285
 amdgpu_atom_execute_table+0x5d/0x72
 transmitter_control_v1_5+0xef/0x11a
 hwss_edp_backlight_control+0x132/0x151
 dce110_disable_stream+0x133/0x16e
 core_link_disable_stream+0x1c5/0x23b
 dce110_reset_hw_ctx_wrap+0xb4/0x1aa
 dce110_apply_ctx_to_hw+0x4e/0x6da
 ? generic_reg_get+0x1f/0x33
 dc_commit_state+0x33f/0x3d2
 amdgpu_dm_atomic_commit_tail+0x2cf/0x5d2
 ? wait_for_common+0x5b/0x69
 commit_tail+0x42/0x64
 drm_atomic_helper_commit+0xdc/0xf9
 drm_atomic_helper_set_config+0x5c/0x76
 __drm_mode_set_config_internal+0x64/0x105
 drm_mode_setcrtc+0x474/0x56f
 ? drm_mode_getcrtc+0x155/0x155
 drm_ioctl_kernel+0x6c/0xa8
 drm_ioctl+0x267/0x353
 ? drm_mode_getcrtc+0x155/0x155
 amdgpu_drm_ioctl+0x4f/0x7f
 vfs_ioctl+0x21/0x2f
 do_vfs_ioctl+0x4c4/0x4e7
 ? security_file_ioctl+0x3b/0x4f
 SyS_ioctl+0x57/0x79
 do_syscall_64+0x64/0x72
 entry_SYSCALL_64_after_hwframe+0x3d/0xa2

V2: Added stack trace in commit message.
Signed-off-by: Shirish S <shirish.s@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>