x86: Use kernel specific subtarget configurations

This makes it possible to use different sub target configurations for
kernel 4.19 for example.
To support kernel 4.9 and kernel 4.14 with the same configuration file
already needed some extra work this will not be needed for kernel 4.19
any more.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>

diff --git a/target/linux/x86/64/config-default b/target/linux/x86/64/config-4.14
similarity index 100%
rename from target/linux/x86/64/config-default
rename to target/linux/x86/64/config-4.14

diff --git a/target/linux/x86/generic/config-default b/target/linux/x86/generic/config-4.14
similarity index 100%
rename from target/linux/x86/generic/config-default
rename to target/linux/x86/generic/config-4.14

diff --git a/target/linux/x86/geode/config-default b/target/linux/x86/geode/config-4.14
similarity index 100%
rename from target/linux/x86/geode/config-default
rename to target/linux/x86/geode/config-4.14

diff --git a/target/linux/x86/legacy/config-default b/target/linux/x86/legacy/config-4.14
similarity index 100%
rename from target/linux/x86/legacy/config-default
rename to target/linux/x86/legacy/config-4.14