defconfigs: add the _AT_LEAST_X_Y headers options

Since commit 2a5cf5e7 (check kernel headers version), we also need to
specify the series of the custom kernel headers version.

The defconfigs file that define such a custom kernel headers version
now fail to build.

Add the required _AT_LEAST_X_Y options to those config files. Done with
this (convoluted but very fast, uch faster ythan manual editing!) rule:

    for f in $( git grep -l BR2_DEFAULT_KERNEL_VERSION=\"3 ); do
        grep -E '^BR2_PACKAGE_HOST_LINUX_HEADERS_CUSTOM_' "${f}" >/dev/null && continue
        sed -r -e '/^(BR2_DEFAULT_KERNEL_VERSION="3\.([[:digit:]]+).*")$/s//\1\nBR2_PACKAGE_HOST_LINUX_HEADERS_CUSTOM_3_\2=y/' "${f}"
    done

Only kernels >= 3.0 need those options in the defconfig, since the
default for 2.6.x kernels is correct (selects _AT_LEAST_2_6), and
the default is not saved in a defconfig.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>