gdb: not available on ARM noMMU and OpenRISC
Neither gdb nor gdbserver have support for ARM noMMU and OpenRISC, so
let's disable gdb on those architectures.
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
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Changes since v2:
- Fixed BR2_openrisc to BR2_or1k in Config.in.host
Changes since v1:
- Fixed BR2_openrisc to BR2_or1k