drivers: Convert to use DT_INST_FOREACH

Convert drivers that have the following pattern:

   #if DT_INST_NODE_HAS_PROP(0, label)
   INIT_MACRO(0)
   #endif

   ...

   #if DT_INST_NODE_HAS_PROP(n, label)
   INIT_MACRO(n)
   #endif

to use DT_INST_FOREACH(INIT_MACRO) instead.

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>