kfifo: remove support for physically non-contiguous memory

kfifo: remove support for physically non-contiguous memory

First, there is no such user. The only user of this interface is
caam_rng_fill_async() and that uses kfifo_alloc() -> kmalloc().

Second, the implementation does not allow anything else than direct
mapping and kmalloc() (due to virt_to_phys()), anyway.

Therefore, there is no point in having this dead (and complex) code in
the kernel.

Note the setup_sgl_buf() function now boils down to simple sg_set_buf().
That is called twice from setup_sgl() to take care of kfifo buffer
wrap-around.

setup_sgl_buf() will be extended shortly, so keeping it in place.

Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Stefani Seibold <stefani@seibold.net>
Link: https://lore.kernel.org/r/20240405060826.2521-5-jirislaby@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>