sdmmc: add example for initializing sdcard

[jakezhu9]

Hi all,

Over the past few weeks, I've developed a demo program to interface with SDHC peripherals. The current version successfully initializes the peripherals and SD cards, reads the CID register, and outputs the results. The program has been tested and runs on the development board(nezha-d1), with the output shown below:

Key Challenges and Solutions:

1. SDHC Peripheral Configuration:
   Configuring SDHC peripherals involved selecting the appropriate clock source and calculating parameters accurately. The oreboot project helped as a reference. I also encountered a register operation bug that took some time to find, and it is now fixed.

2. SDIO Protocol Operation:
   Implementing SD card data read and write functionality using the SDIO protocol presented complexity, particularly with version compatibility and edge cases. Since no Rust crate currently supports this, I have implemented basic initialization and CID register reading for now. Future improvements could include expanding functionality or developing a general SDIO protocol library for broader use.

3. Flashing and Running the Program:
   After compiling, the program requires a correct image header and burning using the xfel tool. I referred to the steps in [board] Rust serial output example and light up led on 100ask-d1-h YuzukiHD/SyterKit#129 to complete.

Reference

oreboot/oreboot#636
oreboot/oreboot#701
YuzukiHD/SyterKit#143
YuzukiHD/SyterKit#129

I believe that this demo will support future boot program development and help adapt frameworks like Rust SyterKit :)

[jakezhu9]

cc @luojia65

[luojia65]

It's a great achievement, thanks a lot!
LGTM