Move LoadKernelOrGetPtr into :redzone_allocator
Move LoadKernelOrGetPtr into :redzone_allocator

The function is only used by the redzone allocator
and has no tests, so it's basically an implementation
detail of the redzone allocator.

After this change `asm_compiler.h` and its target does
not depend anymore on any CUDA specific code.

Note that this adds another `if GOOGLE_CUDA` to the
redzone allocator. This will be fixed in a follow up change.
