regmap: Updates for v4.9

Another quiet release, a few small extensions to the set of register
maps we support and an improvement in the debugfs code:

 - Allow viewing of cached contents for write only registers via
   debugfs.
 - Support a wider range of read/write flag masks in register formats.
 - Support more little endian formats.
Merge remote-tracking branches 'regmap/topic/core' and 'regmap/topic/debugfs' into regmap-next