soc/qman: Change remaining contextB into context_b

There are multiple occurences of both contextB and context_b
in different h/w descriptors, referring to the same descriptor
field known as "Context B". Stick with the "context_b" naming,
for obvious reasons including consistency (see also context_a).

Signed-off-by: Claudiu Manoil <claudiu.manoil@nxp.com>
Signed-off-by: Scott Wood <oss@buserror.net>