etnaviv: Set shader instruction area correctly for GC3000

etnaviv: Set shader instruction area correctly for GC3000

- Use the same instruction area on GC3000 as the Vivante driver.
  This allows the same number of instructions on GC3000 as GC2000
  instead of half.

- Makes sure that the "PE to FE" stall before updating the shader code
  or constants is hit (which is conditional on vs_offset > 0x4000). This
  is necessary on GC3000 too, it increases stability.

Signed-off-by: Wladimir J. van der Laan <laanwj@gmail.com>
Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>