README.mpc85xx-sd-spi-boot: Suggest the NXP boot format github repo

As explained in the text at the bottom of the page
https://source.codeaurora.org/external/qoriq/qoriq-yocto-sdk/boot-format:

"QUIC repositories on this site will not receive any updates after
March 31, 2022, and will be deleted on March 31, 2023."

Point to the NXP boot format github repo instead.

Signed-off-by: Fabio Estevam <festevam@denx.de>
Reviewed-by: Pali Rohár <pali@kernel.org>
diff --git a/doc/README.mpc85xx-sd-spi-boot b/doc/README.mpc85xx-sd-spi-boot
index 329de4e..7608fc3 100644
--- a/doc/README.mpc85xx-sd-spi-boot
+++ b/doc/README.mpc85xx-sd-spi-boot
@@ -14,7 +14,7 @@
 ========================
 
 you can browse it online at:
-https://source.codeaurora.org/external/qoriq/qoriq-yocto-sdk/boot-format
+https://github.com/nxp-qoriq-yocto-sdk/boot-format
 
 Building
 ========