package/linux-headers: restrict versions available on C-SKY

The C-SKY architecture was merged in the upstream Linux kernel
4.20. Therefore, kernel headers from a Linux version earlier than that
cannot be used to build a C-SKY toolchain.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/linux-headers/Config.in.host

@@ -29,20 +29,24 @@ config BR2_KERNEL_HEADERS_AS_KERNEL
 config BR2_KERNEL_HEADERS_4_4
 	bool "Linux 4.4.x kernel headers"
 	depends on !BR2_riscv
+	depends on !BR2_csky
 	select BR2_TOOLCHAIN_HEADERS_AT_LEAST_4_4
 
 config BR2_KERNEL_HEADERS_4_9
 	bool "Linux 4.9.x kernel headers"
 	depends on !BR2_riscv
+	depends on !BR2_csky
 	select BR2_TOOLCHAIN_HEADERS_AT_LEAST_4_9
 
 config BR2_KERNEL_HEADERS_4_14
 	bool "Linux 4.14.x kernel headers"
 	depends on !BR2_riscv
+	depends on !BR2_csky
 	select BR2_TOOLCHAIN_HEADERS_AT_LEAST_4_14
 
 config BR2_KERNEL_HEADERS_4_19
 	bool "Linux 4.19.x kernel headers"
+	depends on !BR2_csky
 	select BR2_TOOLCHAIN_HEADERS_AT_LEAST_4_19
 
 config BR2_KERNEL_HEADERS_5_0