drm/amdkfd: Increase SMI event fifo size

SMI event fifo size 1KB was enough to report GPU vm fault or reset
event, but could drop the more frequent SVM migration events. Increase
kfifo size to 8KB to store about 100 migrate events, less chance to drop
the migrate events if lots of migration happened in the short period of
time. Add KFD prefix to the macro name.

Signed-off-by: Philip Yang <Philip.Yang@amd.com>
Reviewed-by: James Zhu <James.Zhu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>