drm/amdkfd: mark local functions as static

The file was newly added and causes some -Wmissing-prototype warnings:

drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gc_9_4_3.c:57:5: error: no previous prototype for 'kgd_gfx_v9_4_3_hqd_sdma_load' [-Werror=missing-prototypes]
drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gc_9_4_3.c:126:5: error: no previous prototype for 'kgd_gfx_v9_4_3_hqd_sdma_dump' [-Werror=missing-prototypes]
drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gc_9_4_3.c:163:6: error: no previous prototype for 'kgd_gfx_v9_4_3_hqd_sdma_is_occupied' [-Werror=missing-prototypes]
drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gc_9_4_3.c:181:5: error: no previous prototype for 'kgd_gfx_v9_4_3_hqd_sdma_destroy' [-Werror=missing-prototypes]

Mark these all as 'static' since there are no outside callers.

Fixes: a805889a ("drm/amdkfd: Update SDMA queue management for GFX9.4.3")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>