drm/amdkfd: Increase the size of the memory reserved for the TBA

In a future commit, the cwsr trap handler code size for gfx10.1 will
increase to slightly above the one page mark. Since the TMA does not
need to be page aligned, and only 2 pointers are stored in it, push
the TMA offset by 2 KiB and keep the TBA+TMA reserved memory size
to two pages.

Signed-off-by: Laurent Morichetti <laurent.morichetti@amd.com>
Reviewed-by: Felix Kuehling <felix.kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>