u-boot-extra.inc: Rework MicroBlaze config.mk generation
u-boot-extra.inc: Rework MicroBlaze config.mk generation

* Rework the config.mk for MicroBlaze into a seperate task
* Change to using a python task for better handling of content and
  parsing of the xparameters file

Signed-off-by: Nathan Rossi <e1e6d173c6873c0ae2b831215d22380d293bb314@xilinx.com>

nathanrossi/meta-xilinx,nathanrossi/meta-xilinx,Xilinx/meta-xilinx,nathanrossi/meta-xilinx,Xilinx/meta-xilinx,Xilinx/meta-xilinx,Xilinx/meta-xilinx,nathanrossi/meta-xilinx,Xilinx/meta-xilinx,Xilinx/meta-xilinx