MAKEALL: Add -m/-M option to determine maintainers

The -m option tries to find the board in MAINTAINERS file and figure out the
email. The -M option lists boards including their maintainers emails and all
affiliated emails. There are multiple strategies used to retrieve these emails:

1) Check board/<boardname> with git log and use three most recent emails
2) Check board/<boardname> with git log and use three most used emails
3) Try finding board in MAINTAINERS file and retrieve all emails from there

The result is then sorted and unique results are retrieved and reported.

For -m option, only strategy 3) is used.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Wolfgang Denk <wd@denx.de>