m4/as-linux.m4: don't use backported pcmcia_loop_tuple()

m4/as-linux.m4: don't use backported pcmcia_loop_tuple()

Red Hat backported pcmcia_loop_tuple() from 2.6.33 to their 2.6.32
kernel (at least in RHEL6) but they use it in hardly anything, and kept
the older configuration mechanism from 2.6.28 involving
pcmcia_get_first_tuple() and pcmcia_get_next_tuple() macros.

Since they didn't change the prototypes of other functions such as
pcmcia_request_window() or pcmcia_map_mem_page() at the same time as
backporting pcmcia_loop_tuple(), our code that uses those functions in
the callback function passed to pcmcia_loop_tuple() fails to compile for
these Red Hat 2.6.32 kernels.

Change the COMEDI_CHECK_PCMCIA_LOOP_TUPLE configuration test to ignore
pcmcia_loop_tuple() if the pcmcia_get_first_tuple() macro is defined.
This will cause our comedi PCMCIA drivers to use the older configuration
mechanism from the 2.6.28 kernel instead of attempting to use the
broken, backported mechanism.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>