anv: Fix running very large shaders in Gen9 and Gen11
There's a new test in Vulkan CTS 188.8.131.52
dEQP-VK.ssbo.phys.layout.random.16bit.scalar.13 that surfaced two issues:
- A bug in anv_allocator when growing the a pool that had no allocation.
- The limit of allocation is 1MB but in ICL that test has a shader that compiles to more than that.