drm/xe: Stop accepting value in xe_migrate_clear

drm/xe: Stop accepting value in xe_migrate_clear

Although xe_migrate_clear() has a value argument, currently the driver
is only passing 0 at all the places this function is invoked with the
exception the kunit tests are using the parameter to validate this
function with different values.
xe_migrate_clear() is failing on platforms with link copy engines
because xe_migrate_clear() via emit_clear() is using the blitter
instruction XY_FAST_COLOR_BLT to clear the memory. But this instruction
is not supported by link copy engine.
So the solution is to use the alternate instruction MEM_SET when
platform contains link copy engine. But MEM_SET instruction accepts only
8-bit value for setting whereas the value agrument of xe_migrate_clear()
is 32-bit.
So instead of spreading this limitation around all invocations of
xe_migrate_clear() and causing more confusion, it was decided to not
accept any value itself as driver does not really need this currently.

All the kunit tests are adapted as per the new function prototype.

This will be followed by a patch to add support for link copy engines.

Signed-off-by: Balasubramani Vivekanandan <balasubramani.vivekanandan@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>