Fix typos in comment blocks

[Thomas: fix issues noticed by Arnout:
  - Rewrap the linux/Config.in paragraph
  - Revert the "is a toolchain dependency" -> "has a toolchain
    dependency" change from pkg-generic.mk, as the original was
    correct.]

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>