board: ti: Update AM65x and J721e READMEs for OSPI boot

Update AM65x and J721e README files with instructions for flashing OSPI
images.

Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
diff --git a/board/ti/j721e/README b/board/ti/j721e/README
index 5be7d09..739d493 100644
--- a/board/ti/j721e/README
+++ b/board/ti/j721e/README
@@ -225,3 +225,50 @@
                 | |    Secure config  | |
                 | +-------------------+ |
                 +-----------------------+
+
+OSPI:
+-----
+ROM supports booting from OSPI from offset 0x0.
+
+Flashing images to OSPI:
+
+Below commands can be used to download tiboot3.bin, tispl.bin, u-boot.img,
+and sysfw.itb over tftp and then flash those to OSPI at their respective
+addresses.
+
+=> sf probe
+=> tftp ${loadaddr} tiboot3.bin
+=> sf update $loadaddr 0x0 $filesize
+=> tftp ${loadaddr} tispl.bin
+=> sf update $loadaddr 0x80000 $filesize
+=> tftp ${loadaddr} u-boot.img
+=> sf update $loadaddr 0x280000 $filesize
+=> tftp ${loadaddr} sysfw.itb
+=> sf update $loadaddr 0x6C0000 $filesize
+
+Flash layout for OSPI:
+
+         0x0 +----------------------------+
+             |     ospi.tiboot3(512K)     |
+             |                            |
+     0x80000 +----------------------------+
+             |     ospi.tispl(2M)         |
+             |                            |
+    0x280000 +----------------------------+
+             |     ospi.u-boot(4M)        |
+             |                            |
+    0x680000 +----------------------------+
+             |     ospi.env(128K)         |
+             |                            |
+    0x6A0000 +----------------------------+
+	     |	 ospi.env.backup (128K)   |
+	     |                            |
+    0x6C0000 +----------------------------+
+             |      ospi.sysfw(1M)        |
+             |                            |
+    0x7C0000 +----------------------------+
+	     |      padding (256k)        |
+    0x800000 +----------------------------+
+             |     ospi.rootfs(UBIFS)     |
+             |                            |
+             +----------------------------+