spmi: regmap: enable userspace writes

Being able to write to spmi registers via userspace is required
for quick debug and development. Enable it.

The regmap framework uses dev_name to create debugfs dir names.
So update the spmi devices to have proper names.

Change-Id: I8a5da203b212df9a7f1410e3fcf6ee7b429856b6
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>