debug/gdb: hide Linaro options by default

It can be quite confusing for a new-comer to find strange
version numbers for gdb, so hide the Linaro versions by
default.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

# Linux kernel options

config KERNEL_linux

    select KERNEL_SUPPORTS_SHARED_LIBS

    help

      Build a toolchain targeting systems running Linux as a kernel.