package/arm-gnu-toolchain: revert to version 10

Revert the toolchain to version 10.x because of bug in 11.x:
when the pre-packaged GCC was built, it could be targeting
a newer x86_64 architecture than the processor being used.
Confirmed fix will be implemented in the next release:

https://bugs.linaro.org/show_bug.cgi?id=5825#c19
Signed-off-by: Xuanhao Shi <x-shi@ti.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>