doc: board: Convert README.sh7752evb to reST

Convert plain text documentation to reStructuredText format and add
it to Sphinx TOC tree. No essential content change.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/doc/board/index.rst b/doc/board/index.rst
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--- a/doc/board/index.rst
+++ b/doc/board/index.rst
@@ -11,4 +11,5 @@
    emulation/index
    google/index
    intel/index
+   renesas/index
    sifive/index
diff --git a/doc/board/renesas/sh7752evb.rst b/doc/board/renesas/sh7752evb.rst
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+.. SPDX-License-Identifier: GPL-2.0+
+
+R0P7752C00000RZ board
+=====================
+
+This board specification
+------------------------
+
+The R0P7752C00000RZ(board config name:sh7752evb) has the following device:
+
+ - SH7752 (SH-4A)
+ - DDR3-SDRAM 512MB
+ - SPI ROM 8MB
+ - Gigabit Ethernet controllers
+ - eMMC 4GB
+
+
+Configuration for This board
+----------------------------
+
+You can select the configuration as follows:
+
+ - make sh7752evb_config
+
+
+This board specific command
+---------------------------
+
+This board has the following its specific command:
+
+write_mac:
+  You can write MAC address to SPI ROM.
+
+Usage 1: Write MAC address
+
+.. code-block:: none
+
+   write_mac [GETHERC ch0] [GETHERC ch1]
+
+   For example:
+   => write_mac 74:90:50:00:33:9e 74:90:50:00:33:9f
+
+* We have to input the command as a single line (without carriage return)
+* We have to reset after input the command.
+
+Usage 2: Show current data
+
+.. code-block:: none
+
+   write_mac
+
+   For example:
+   => write_mac
+      GETHERC ch0 = 74:90:50:00:33:9e
+      GETHERC ch1 = 74:90:50:00:33:9f
+
+
+Update SPI ROM
+--------------
+
+1. Copy u-boot image to RAM area.
+2. Probe SPI device.
+
+.. code-block:: none
+
+   => sf probe 0
+   SF: Detected MX25L6405D with page size 64KiB, total 8 MiB
+
+3. Erase SPI ROM.
+
+.. code-block:: none
+
+   => sf erase 0 80000
+
+4. Write u-boot image to SPI ROM.
+
+.. code-block:: none
+
+   => sf write 0x48000000 0 80000