oxnas: Enable CONFIG_CRYPTO_LZ4

oxnas: Enable CONFIG_CRYPTO_LZ4

Previously, CONFIG_LZ4_DECOMPRESS=y was selected by CONFIG_RD_LZ4 only.

When building kernel for initramfs, CONFIG_RD_LZ4 will be unset by
Kernel/SetInitramfs if the chosen compression method is not lz4, then
CONFIG_LZ4_DECOMPRESS will become a *module* in the newly generated
kernel config.

However, the newly added module won't be built after
38c150612cc9be488527e342db92d5c74093213f, so packaging kmod-lib-lz4
fails due to missing lz4_decompress.ko.

CONFIG_CRYPTO_LZ4=y makes CONFIG_LZ4_DECOMPRESS=y being selected w/o
CONFIG_RD_LZ4, so that the modules of the default kernel and initramfs
kernel are consistent.

Fixes: #12766
Fixes: 38c150612cc ("build: revert 54070a1 (all kernels are >= 5.10)")
Signed-off-by: Jitao Lu <dianlujitao@gmail.com>