The default channel configuration is managed within the Makefiles of many
examples and tests. This commit moves the default channel logic to
`makefiles/default-channel.ink.mk` to ease maintenance. All Makefiles that
previously managed the default channel configuration themself have been
updated to include that file.
The default channel configuration of the cc110x has been added
Adding saml1[01]-xpro, nucleo-f302r8|f334r8 to
BOARDS_INSUFFICIENT_MEMORY.
The riotboot build fails because it only offers half the flash size (per
slot), compared to before where the default build would not use riotboot
at all, thus have double the flash (but being useless).
