bitbake: fetch/hg: support submodules

bitbake: fetch/hg: support submodules

Use hg clone and hg pull to copy the source into the build
directory rather than taring up the cloned repository and
untarring in the destination.

This allows submodules to be cloned. While here, make the default
behaviour keep the hg scm data to match the behaviour of the git
fetcher.

(Bitbake rev: f002b1ca80cb542a4ed0c06c53c914cd5e076565)

Signed-off-by: Daniel McGregor <daniel.mcgregor@vecima.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>