Use __attribute__((visibility("hidden"))) for __ncr_file_descriptor to
take advantage of PIC addressing instead of going through the dynamic
linker.  Add an internal alias for ncr_global_init() for the same
reason.

Add an internal header file to consolidate the "extern" references in
the process.

Let <ncrypto.h> users #include this header file alone, without caring
about <linux/ncr.h>.

To do so, set up a temporary copy of ncr.h so that the
	#include <linux/ncr.h>
works at build time as well.

on keys to read/write to prevent overwriting a key while using it. Several
other cleanups.