Change to zstd compressed instead of gz-compressed tarballs. zstd
compresses 7-8 times faster and decompresses 2-3 times faster.
This change also make sharing tarballs between different branches
possible, because OpenWrt 25.12 uses zstd as default.
Signed-off-by: Andreas Gnau <andreas.gnau@iopsys.eu>
This is no longer necessary since feeds/broadcom commit 3191be5482a8
(bcmkernel: toolchain: Set more flags and tools, 2024-04-17).
Signed-off-by: Andreas Gnau <andreas.gnau@iopsys.eu>
