toolchain/gdb: disable support of full gdb on target for blackfin

There is no support in gdb 6.6 for the Blackfin architecture, so
disallow this choice. This fixes the following build failure:

  http://autobuild.buildroot.org/results/e37db29810265a756833da163fda444d967d7874/build-end.log

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

toolchain/gdb/Config.in

@@ -4,7 +4,7 @@ config BR2_PACKAGE_GDB
 	bool "Build gdb debugger for the Target"
 	select BR2_PACKAGE_NCURSES
 	depends on BR2_USE_WCHAR
-	depends on !BR2_sh && !BR2_sh64 && !BR2_avr32 && !BR2_microblaze
+	depends on !BR2_sh && !BR2_sh64 && !BR2_avr32 && !BR2_microblaze && !BR2_bfin
 	# The newest versions of gdb require thread debugging in the
 	# toolchain. The only cases for which this is not needed is if
 	# we use gdb 6.8 (marked deprecated)