radix tree test suite: Add kmem_cache enhancements and pr_err

radix tree test suite: Add kmem_cache enhancements and pr_err

Add kmem_cache_set_non_kernel(), a mechanism to allow a certain number
of kmem_cache_alloc requests to succeed even when GFP_KERNEL is not set
in the flags.

Add kmem_cache_get_alloc() to see the size of the allocated kmem_cache.

Add a define of pr_err to printk.

Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>