drm/amdkfd: Consolidate duplicated bo alloc flags

ALLOC_MEM_FLAGS_* used are the same as the KFD_IOC_ALLOC_MEM_FLAGS_*,
but they are interweavedly used in kernel driver, resulting in bad
readability. For example, KFD_IOC_ALLOC_MEM_FLAGS_COHERENT is not
referenced in kernel, and it functions implicitly in kernel through
ALLOC_MEM_FLAGS_COHERENT, causing unnecessary confusion.

Replace all occurrences of ALLOC_MEM_FLAGS_* with
KFD_IOC_ALLOC_MEM_FLAGS_* to solve the problem.

Signed-off-by: Yong Zhao <Yong.Zhao@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>