mailbox: bcm-flexrm-mailbox: Use bitmap instead of IDA
Currently, we are using IDA library for managing IDs
on a FlexRM ring. The IDA library dynamically allocates
memory for underlying data structures which can cause
potential locking issue when allocating/free IDs from
flexrm_new_request() and flexrm_process_completions().
To tackle this, we replace use of IDA with bitmap for
each FlexRM ring and also protect the bitmap with FlexRM
ring lock.