drm/amd/display: Calculate swizzle mode using bpp during validation

[Why]
Previously bandwidth validation was failing because swizzle mode was not
initialized during plane_state allocation. The swizzle mode was
calculated using pixed format which is how swizzle mode is initially
calculated in addrlib.

[How]
* Set default swizzle mode for validation to DC_SW_UNKNOWN
* Created new function in dcn10_assign_swizzle_mode which sets the
  plane swizzle mode based on selected pixed format
* Added the call of assign_swizzle_mode into dc_validate_global_state
* Set failsafe swizzle mode back to DC_SW_LINEAR

Signed-off-by: Su Sung Chung <Su.Chung@amd.com>
Reviewed-by: Eric Yang <eric.yang2@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>