lirc_rpi: GPIO-based Lirc driver for Raspberry Pi

This code is a further development of the Lirc driver for the Raspberry Pi by Aron Szabo, which was derived from the Lirc serial driver.

The added features are: Multiple transmitter support, support for "modulation frequency 0", and the programmable inversion of outputs.

It is described in greater detail in this article (not quite up-to-data). Please also see this article for possible hardware.

The original work is copyrighted under the GNU General Public License, version 2 "or later". Being a derived work, this goes for my version too.

Update 2016-12-06

Updated for current Raspberry Pi OS, including device tree (the file lirc-rpi-overlay.dts). Tested with Raspian May 2016 kernel 4.4.11-v7+. Changes:

• The option gpio_out_pins has been renamed to gpio_out_pin (singular), to be compatible by the original lirc_rpi. Suggested by Aron.
• New option gpio_in_pull (from the Raspian lirc_rpi).
• The option tx_mask has been removed (not really a module parameter, but a user parameter).
• Support for devicetree; the new file lirc-rpi-overlay.dts. (Note the hyphens; there is an underscore in lirc_rpi.) Note that the actually used pins (or a superset thereof) have to be defined in this file, which is subsequently compiled, for example when building the kernel.

Update 2017-07-05

Verified that the current version compiles and runs on the current official Raspian (with 4.9 kernel). In the light of issue 8 create a version that runs with the new media distribution. This is checked in into the media branch.