[RFC] Add ff-memless-next driver

[Michal Malý]

Hi,

"ff-memless-next" driver is an extended modification of the original ff-memless driver. Unlike ff-memless, ff-memless-next targets only "serious" FFB devices such as racing wheels and hi(ish)-end joysticks with FFB actuators instead of simple rumble motors. Modifications in ff-memless-next include:
- Support of periodic and ramp effects
  These are treated as "combinable" effects and forces created by each of these effects is superposed into one total force
- Support for conditional effects
  As these effects cannot be effectively combined together, they are handled separately depending on the capabilities of the underlying HW-specific driver
- Removed emulation of rumble effect
- Adjustable update rate
- Differentiation between "set effect's force to zero" and "stop effect"
- Checks whether the effect's parameters are valid upon upload - this should better be handled by ff-core though IMHO.

At the moment there is no HW-specific backend that would make use of ff-memless-next, the plan is to update hid-lg4ff once ff-memless-next gets accepted by upstream. ff-memless-next can be tested with dummy FFB device module which is available here (git://prifuk.cz/ff-dummy-device).

My primary motivation to write ff-memless-next were limitations of the current ff-memless driver I came across during work on the driver for Logitech gaming wheels. However, ff-memless-next contains no code that would specifically target Logitech devices.

I must give a huge thanks to Elias Vanderstuyft (CC'd) for his extensive testing of the driver and numerous helpful suggestions.

Tested-by: Elias Vanderstuyft <elias.vds@xxxxxxxxx>
Signed-off-by: Michal Malý <madcatxster@xxxxxxxxx>
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