base.bbclass: Combine all checksum.ini files found in BBPATH
base.bbclass: Combine all checksum.ini files found in BBPATH

This makes it possible for overlays to have checksum.ini.

Signed-off-by: Petri Lehtinen <ded098e9a5465cb2f969d4bc09b4ab7ed3e4945d@inoi.fi>

mrchapp/arago-da830,mrchapp/arago-da830,mrchapp/arago-da830