powerpc/BSR: Support multiple OF-node description of BSR

This adds support for multiple BSR nodes in the OF device tree.

Previously, the BSR driver only supported a single OF node describing
a BSR.  Apparently when an LPAR is set to use "all system resources"
the BSR appears as a single node, but when it is handed out in pieces,
each 8 byte piece gets its own node.  So, this keeps a list of BSR
devices instead of the array and includes all nodes.

Also, this makes the code be more inclusive of what BSR devices we
accept by only checking compatibility and not the device name property
(which might change in the future versions of BSR).

Signed-off-by: Sonny Rao <sonnyrao@us.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>