zephyr: alloc: rename to alloc_impl

The alloc crate conflicts with the name of the alloc module.  Resolve
this by renaming our module to `alloc_impl` to better suggest it's
purpose.

Signed-off-by: David Brown <[email protected]>

Author: d3zd3z

zephyr/src/alloc.rs renamed to zephyr/src/alloc_impl.rs

@@ -133,4 +133,4 @@ pub mod _export {
 // Mark this as `pub` so the docs can be read.
 /// If allocation has been requested, provide the allocator.
 #[cfg(CONFIG_RUST_ALLOC)]
-pub mod alloc;
+pub mod alloc_impl;