drm/amdkfd: update buffer_{store,load}_* modifiers for gfx940

Instruction modifiers of the untyped vector memory buffer instructions
(MUBUF encoded) changed in gfx940.  The slc, scc and glc modifiers have
been replaced with sc0, sc1 and nt.

The current CWSR trap handler is written using pre-gfx940 modifier
names, making the source incompatible with a strict gfx940 assembler.

This patch updates the cwsr_trap_handler_gfx9.s source file to be
compatible with all gfx9 variants of the ISA.  The binary assembled code
is unchanged (so the behaviour is unchanged as well), only the source
representation is updated.

Signed-off-by: Lancelot SIX <lancelot.six@amd.com>
Reviewed-by: Jay Cornwall <jay.cornwall@amd.com>
Acked-by: Felix Kuehling <felix.kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>