vc4: Use Newton-Raphson on the 1/W write to fix glmark2 terrain.
vc4: Use Newton-Raphson on the 1/W write to fix glmark2 terrain.

The 1/W was apparently not accurate enough, and we were getting sparklies
in the distance.  The closed driver also did a N-R step here.

Cc: <59f39c0db42d4479a46b02d4d2bc11120e37bb44@lists.freedesktop.org>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler