drm/amd/display: Convert memory from cpu to fw endianness correctly

[Why]
Current code does not guarantee the correct endianness of memory being
copied to fw, specifically in the case where cpu isn't little endian.

[How]
Windows and Diags are always little endian, so we define a macro that
does nothing. Linux already defines this macro and will do the correct
endianness conversion.

Signed-off-by: Wyatt Wood <wyatt.wood@amd.com>
Reviewed-by: Harry Wentland <Harry.Wentland@amd.com>
Acked-by: Anthony Koo <Anthony.Koo@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>