scripts/extract-ikconfig: Support LZ4-compressed images.

Support for kernel image LZ4 compression was added around 3.11, but not
the corresponding kernel .config extraction.

This makes possible extracting the kernel config for LZ4-compressed
kernels you're not running, or the current LZ4-compressed kernel if
compiled without /proc/config.gz support.
Signed-off-by: Alex Pilon <alp+linux@alexpilon.ca>
Signed-off-by: Michal Marek <mmarek@suse.cz>

scripts/extract-ikconfig

@@ -61,6 +61,7 @@ try_decompress '\3757zXZ\000' abcde unxz
 try_decompress 'BZh'          xy    bunzip2
 try_decompress '\135\0\0\0'   xxx   unlzma
 try_decompress '\211\114\132' xy    'lzop -d'
+try_decompress '\002\041\114\030' xyy 'lz4 -d -l'
 
 # Bail out:
 echo "$me: Cannot find kernel config." >&2