uDMA SDIO doc updates (#353)

* Added pin diagram and CSR details

* Updated architecture section

* Updated register description

* Removed redundant files

* SDIO: Updated block diagram and Rx/Tx operation

* SDIO: Added Firmware guidelines

* SDIO: Deleted redundant files

* SDIO: Fixed indentation

* SDIO: Fixed typos and sentence restructuring

* Added missing diagrams and minor sentence restructuring

* Added missing diagram

Author: cst-aditya