lib: bitfield: new macros for bit processing

lib: bitfield: new macros for bit processing

New macros have been added for the following -
1. to efficiently iterate and execute functions on already set bits
2. to check if a bit is in use
3. to check if a bitfield has been initialized (this is to safetly
handle cases where the bitfield is freed and re-allocated).
4. to check if two bitfields have the same bits set

Signed-off-by: Anuradha Karuppiah <anuradhak@cumulusnetworks.com>