Documentation/platforms/risc-v/eic7700x: Add support for ESWIN EIC7700X SoC

This PR adds support for the ESWIN EIC7700X RISC-V SoC.
This will be used by the upcoming port of NuttX for PINE64 StarPro64 SBC.

Most of the code was derived from NuttX for SOPHGO SG2000 SoC.
The modified code is explained here:
https://lupyuen.github.io/articles/starpro64#appendix-port-nuttx-to-starpro64

platforms/risc-v/eic7700x/index.rst: Added EIC7700X SoC

Signed-off-by: Lup Yuen Lee <luppy@appkaki.com>

Documentation/platforms/risc-v/eic7700x/index.rst

@@ -0,0 +1,16 @@
+==============
+ESWIN EIC7700X
+==============
+
+`ESWIN EIC7700X <https://www.eswincomputing.com/en/products/index/36.html>`_ is a 64-bit RISC-V SoC with 4 RISC-V Cores:
+
+- **Processors:** 4 x RV64GC 1.4 GHz 64-bit RISC-V Cores
+- **NPU:** 19.95 TOPS INT8
+- **Memory:** Up to 32 GB 64-bit LPDDR4 / 4x / 5
+- **Storage:** eMMC 5.1, 2 x SDIO 3.0, SATA3, SPI NOR Flash
+- **Video Decoding:** H.265 up to 8K @ 50 FPS, or 32 x 1080P @ 30 FPS
+- **Video Encoding:** H.265 up to 8K @ 25 FPS, or 13 x 1080P @ 30 FPS
+- **Image Processing:** JPEG ISO/IEC 10918-1, ITU-T T.81
+- **Network:** 2 x GMAC, RGMII supported
+- **PCI Express:** 4-lane PCIe 3.0 (RC + EP)
+- **Peripherals:** 2 x USB 3.0 DRD (Host + Device), 12 x I2C, 5 x UART, 2 x SPI, 3 x I2S (Slave + Master)