kernel: Add kmod-crypto-xxhash

kxxhash_generic.ko is a soft dependency of kmod-fs-btrfs, but we did not
package it. Extract the kmod-lib-xxhash and then package
xxhash_generic.ko.

Link: https://github.com/openwrt/openwrt/pull/15833
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
(cherry picked from commit 2ebeda0294)
Link: https://github.com/openwrt/openwrt/pull/15898
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>

package/kernel/linux/modules/crypto.mk

@@ -1053,3 +1053,15 @@ endef
 
 $(eval $(call KernelPackage,crypto-xts))
 
+
+define KernelPackage/crypto-xxhash
+  TITLE:=xxHash non-cryptographic hash algorithm
+  DEPENDS:=+kmod-crypto-hash +kmod-lib-xxhash
+  KCONFIG:=CONFIG_CRYPTO_XXHASH
+  FILES:=$(LINUX_DIR)/crypto/xxhash_generic.ko
+  AUTOLOAD:=$(call AutoLoad,09,xxhash_generic)
+  $(call AddDepends/crypto)
+endef
+
+$(eval $(call KernelPackage,crypto-xxhash))
+