buildroot: Move to 2021.02 LTS release

The busybox init patch was refreshed as it did not apply cleanly.

Signed-off-by: Joel Stanley <joel@jms.id.au>
diff --git a/.gitmodules b/.gitmodules
index 499afdf..27c5792 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -1,4 +1,4 @@
 [submodule "buildroot"]
 	path = buildroot
-	branch = 2020.08.2-op-build
+	branch = 2021.02-op-build
 	url = https://github.com/open-power/buildroot