MAINTAINERS: Change L to M for Broadcom ARM/ARM64 SoC entries

bcm-kernel-feedback-list@broadcom.com is a Broadcom internal
mailing-list for which no external subscribers are allowed for now, so
update the different entries from L to M to reflect that and order
entries from M to L in order of preference.

Suggested-by: Arnd Bergmann <arnd@arndb.de>
Suggested-by: Olof Johansson <olof@lixom.net>
Suggested-by: Scott Branden <scott.branden@broadcom.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>