radeon: fix pitch alignment for non-power-of-two mipmaps on SI

radeon: fix pitch alignment for non-power-of-two mipmaps on SI

This fixes VM protection faults.

I have a new piglit test which can iterate over all possible widths, heights,
and depths (including NPOT) and tests mipmapping with various texture targets.

After this is committed, I'll make a new release of libdrm and bump
the libdrm version requirement in Mesa.