package/avrdude: spi needs headers >= 4.8

SPI unconditionally uses GPIOHANDLE_SET_LINE_VALUES_IOCTL which is only
available since kernel 4.8 and
https://github.com/torvalds/linux/commit/d7c51b47ac11e66f547b55640405c1c474642d72
resulting in the following build failure since switch to upstream in
commit 03fa36df7e6aca0f4a1c8ae2fe691c0cda6ddc7a:

linuxspi.c: In function 'linuxspi_reset_mcu':
linuxspi.c:102:28: error: storage size of 'data' isn't known
     struct gpiohandle_data data;
                            ^~~~
linuxspi.c:110:32: error: 'GPIOHANDLE_SET_LINE_VALUES_IOCTL' undeclared (first use in this function)
     ret = ioctl(fd_linehandle, GPIOHANDLE_SET_LINE_VALUES_IOCTL, &data);
                                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Fixes:
 - http://autobuild.buildroot.org/results/769021040e5e9293584734e4f461baeaa6dd91cd

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Reviewed-by: Yegor Yefremov <yegorslists@googlemail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

package/avrdude/Config.in

@@ -20,10 +20,10 @@ if BR2_PACKAGE_AVRDUDE
 config BR2_PACKAGE_AVRDUDE_SPI
 	bool "SPI support"
 	default y # Backward compatibility
-	depends on BR2_TOOLCHAIN_HEADERS_AT_LEAST_4_6
+	depends on BR2_TOOLCHAIN_HEADERS_AT_LEAST_4_8
 
-comment "SPI support needs a toolchain w/ linux headers >= 4.6"
-	depends on !BR2_TOOLCHAIN_HEADERS_AT_LEAST_4_6
+comment "SPI support needs a toolchain w/ linux headers >= 4.8"
+	depends on !BR2_TOOLCHAIN_HEADERS_AT_LEAST_4_8
 
 endif