MAINTAINERS.yml: Add myself as ARM collaborator

Currently the Cortex-R platform has no one watching over it.  Submitting
myself to help with the Cortex-R parts of the ARM architecture.

Signed-off-by: Bradley Bolen <bbolen@lexmark.com>

Author: Bradley Bolen

MAINTAINERS.yml

@@ -135,6 +135,7 @@ ARM arch:
         - galak
         - MaureenHelm
         - stephanosio
+        - bbolen
     files:
         - arch/arm/aarch32/
         - arch/arm/common/