drm/amd/display: Add configurable SPL namespace prefix

drm/amd/display: Add configurable SPL namespace prefix

[WHY]
SPL is a shared library that is used both in kernel and userspace.
When multiple libraries use SPL as statically linked, namespace
collision occur.

[HOW]
Create a configurable namespace prefix.
Add the prefix to all the public functions of the library to
distinguish between the SPL functions in each library.

Reviewed-by: Samson Tam <samson.tam@amd.com>
Signed-off-by: Navid Assadian <Navid.Assadian@amd.com>
Tested-by: Dan Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>