callouts: refactor: merge i2c and fsi callouts

Merge gen_i2c_callouts.pl and gen_proc_fsi_callouts.pl to a single
gen_callouts.pl.

The idea as to have a unified output generated for callouts,
irrespective of bus type. The output will be in YAML, as follows:

<sysfs path> : <Inventory path to be called out>

This will simplify usage for the FRU management code, as well as it
should be easier to support other bus types.

Change-Id: I8793be1207d905af1eb83b5b04383da39efbe02f
Signed-off-by: Deepak Kodihalli <dkodihal@in.ibm.com>
3 files changed