buildroot

configs: switch to a wget download for kernels on github

The linux git trees on github can be huge, and takes a long time to
download, which is not very nice nor convenient for newcomers.

Switch them to using a wget, with the github macro.

A nice side effect of this conversion, is that we no longer need to wait
for the git clone to finish to notice that the ref is gone; doing a wget
will instantly fail in that case.

Mechanical patch, obtained by running (hang-on tight):

$ sed -r -i -e 's/BR2_LINUX_KERNEL_CUSTOM_GIT/BR2_LINUX_KERNEL_CUSTOM_TARBALL/; /BR2_LINUX_KERNEL_CUSTOM_REPO_URL/N; s:BR2_LINUX_KERNEL_CUSTOM_REPO_URL="https\://github.com/([^/]+)/(.+)"\nBR2_LINUX_KERNEL_CUSTOM_REPO_VERSION="(.+)":BR2_LINUX_KERNEL_CUSTOM_TARBALL_LOCATION="$(call github,\1,\2,\3)/linux-\3.tar.gz":; s/(call github.*)\.git/\1/;' $(grep -l 'BR2_LINUX_KERNEL_CUSTOM_REPO_URL="https://github.com' configs/*)

olimex_a20_olinuxino_lime_mali had a comment in between, so it was
manually fixed thereafter; that comment was also moved.

Except for socrates_cyclone5 which did not work previously (missing tag
in git tree?), all the affected defconfigs still download their sources.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>