bcm63xx-cfe: fix build with CONFIG_AUTOREMOVE

When CONFIG_AUTOREMOVE is enabled, CFE binaries are removed before the
image creation.
Install CFE binaries to kernel directory and let autoremove clean the
files in PKG_BUILD_DIR.
Also drop unneeded tar cmd/options.

Fixes: dcee4eaa42 ("bcm63xx-cfe: add package with CFE RAM binaries")
Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>

package/kernel/bcm63xx-cfe/Makefile

@@ -2,7 +2,7 @@ include $(TOPDIR)/rules.mk
 include $(INCLUDE_DIR)/kernel.mk
 
 PKG_NAME:=bcm63xx-cfe
-PKG_RELEASE:=1
+PKG_RELEASE:=2
 
 PKG_SOURCE_URL:=https://github.com/openwrt/bcm63xx-cfe.git
 PKG_SOURCE_PROTO:=git
@@ -10,15 +10,10 @@ PKG_SOURCE_DATE:=2020-05-18
 PKG_SOURCE_VERSION:=efe3b81121a84c0b8ba6a7d0d47cd5eeeb23808d
 PKG_MIRROR_HASH:=299dcf6ef1ad034df26daee6446b574abcd7526a2fe90fb8115890e71bc0d58b
 
-PKG_BUILD_DIR:=$(KERNEL_BUILD_DIR)/$(PKG_NAME)
-
 PKG_FLAGS:=nonshared
 
 include $(INCLUDE_DIR)/package.mk
 
-TAR_OPTIONS:=--strip-components 1 $(TAR_OPTIONS)
-TAR_CMD=$(HOST_TAR) -C $(1) $(TAR_OPTIONS)
-
 define Package/bcm63xx-cfe
   SECTION:=boot
   CATEGORY:=Boot Loaders
@@ -39,4 +34,10 @@ define Package/bcm63xx-cfe/install
 	true
 endef
 
+define Build/InstallDev
+	rm -rf $(KERNEL_BUILD_DIR)/$(PKG_NAME)
+	mkdir -p $(KERNEL_BUILD_DIR)/$(PKG_NAME)
+	$(CP) -r $(PKG_BUILD_DIR)/* $(KERNEL_BUILD_DIR)/$(PKG_NAME)
+endef
+
 $(eval $(call BuildPackage,bcm63xx-cfe))