winsys/amdgpu: calculate the maximum number of compute units
winsys/amdgpu: calculate the maximum number of compute units

Required for register spilling.

Cc: 11.0 <59f39c0db42d4479a46b02d4d2bc11120e37bb44@lists.freedesktop.org>
Reviewed-by: Alex Deucher <08dc22c6156113f2deff178e35e3ed9b24d6af9e@amd.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler