iio: accel: st_accel: Add lis3l02dq support

iio: accel: st_accel: Add lis3l02dq support

Time to finally kill off the venerable (it was one of my first drivers)
lis3l02dq driver in favour of adding support in the st sensors framework.

This does loose us the event support that driver always had, but I think
that will reappear at some point and in the meantime the maintenance
advantages of dropping the 'special' driver for this one part outweigh
the issues.

It's worth noting this part is ancient and I may well be the only person
who still has any on hardware running recent kernels.

It has a few 'quirks'.
 - No WAI register so that just became optional.
 - A BDU option that really does block updates.  Completely.
   Whatever you do, you don't get any more data with it set.
   It is documented the same as more modern parts but I presume they
   are actually clearing for updates after a read of both bytes!
 - Fixed scale.
 - It's too quick.  Even at slowest rate (280Hz) I can't read out fast
   enough on my board (stargate 2) to beat new data coming in. Linus'
   repeat read patch doesn't help in this case. It just means I get 10
   readings before dying... So in reality this will get used with
   software triggers only unless someone has this long out of production
   device on a quick board.

Signed-off-by: Jonathan Cameron <jic23@kernel.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Cc: Denis CIOCCA <denis.ciocca@st.com>
Cc: Crestez Dan Leonard <leonard.crestez@intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>