pitft: Add PiTFT22 support

- Add support to build overlays for PiTFT22 in the kernel.
- Setup a basic configuration for the driver

The PiTFT22 support is optional and can be enabled by adding below in
local.conf:

MACHINE_FEATURES += "pitft pitft22"

This patch also includes restructuring of kernel patches per kernel version
specific directories.

[Support #70]

Signed-off-by: Petter Mabäcker <petter@technux.se>
Signed-off-by: Andrei Gherzan <andrei@gherzan.ro>

README

@@ -226,6 +226,13 @@ MACHINE_FEATURES += "pitft"
 NOTE: To get this working the overlay for the PiTFT model must be build,
       added and specified as well (dtoverlay=<driver> in config.txt)
 
+Below is a list of currently supported PiTFT models in meta-raspberrypi,
+the modelname should be added as a MACHINE_FEATURES in local.conf like below:
+    - MACHINE_FEATURES += "pitft <modelname>"
+
+List of currently supported models:
+    - pitft22
+
 
 4. Extra apps
 =============