support/scripts/gen-bootlin-toolchains: generate BR2_ARCH_NEEDS_GCC_AT_LEAST_X guard

Previously, gen-bootlin-toolchains did not add a `depends` guard to
limit the available toolchains based on the minimum required GCC version
for the user selected CPU tuning.

Now, the proper BR2_ARCH_NEEDS_GCC_AT_LEAST_X guard will be added based
on the version of GCC provided by the toolchain.

Signed-off-by: Vincent Fazio <vfazio@gmail.com>
[yann.morin.1998@free.fr: regenerate the toolchain list]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>