imx: Suggest the NXP ATF github repo

As explained in the text at the bottom of the page
https://source.codeaurora.org/external/imx/imx-atf:

"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 ATF github repo instead.

Signed-off-by: Fabio Estevam <festevam@denx.de>
Reviewed-by: Oliver Graute <oliver.graute@kococonnector.com>
Reviewed-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Reviewed-by: Frieder Schrempf <frieder.schrempf@kontron.de>
diff --git a/board/google/imx8mq_phanbell/README b/board/google/imx8mq_phanbell/README
index 88a136b..7c63fc5 100644
--- a/board/google/imx8mq_phanbell/README
+++ b/board/google/imx8mq_phanbell/README
@@ -10,7 +10,7 @@
 Get and Build the ARM Trusted firmware
 ======================================
 Note: srctree is U-Boot source directory
-Get ATF from: https://source.codeaurora.org/external/imx/imx-atf
+Get ATF from: https://github.com/nxp-imx/imx-atf
 branch: imx_4.19.35_1.0.0
 $ make PLAT=imx8mq bl31
 $ cp build/imx8mq/release/bl31.bin $(builddir)