toolchain/gcc: switch to version 11 by default

toolchain/gcc: switch to version 11 by default

gcc10 seem to increase build size and gcc11 seem to fix that.

Compile tests:
* all

Runtime tests:
* ath79
* mpx85xx/p2020
* mvebu
* x86/64

Special thanks to Rosen for fixing layerscape & bcm63xx

Signed-off-by: Paul Spooren <[email protected]>
Reviewed-by: Rui Salvaterra <[email protected]
Acked-by: Rosen Penev <[email protected]>
Acked-by: Rui Salvaterra <[email protected]
Acked-by: Hauke Mehrtens <[email protected]>
Acked-by: Stijn Tintel <[email protected]>
Acked-by: Aleksander Jan Bajkowski <[email protected]>
Tested-by: Pawel Dembicki <[email protected]>
Tested-by: Aleksander Jan Bajkowski <[email protected]>