bfd: Use size_t in the BFD mmap interface

Change the size type in the BFD mmap interface from bfd_size_type to
size_t to be consistent with the size type of the host mmap interface.

	* bfdio.c (bfd_iovec): Change the bmmap size type to size_t.
	(bfd_mmap): Likewise.
	(memory_bmmap): Likewise.
	* cache.c (cache_bmmap): Change the bmmap size type to size_t.
	* opncls.c (opncls_bmmap): Change the bmmap size type to size_t.
	* bfd-in2.h: Regenerated.
	* libbfd.h: Likewise.