Config.in.legacy: fix removed bootlin riscv64 toolchains
commit b3c66481e1f1503fcbf193d0c780271e880ad500 replaced RISC-V LP64
bootlin toolchains by RISC-V LP64D. However, Config.in.legacy was added
for BR2_TOOLCHAIN_EXTERNAL_BOOTLIN_RISCV64_GLIBC_STABLE, which never
existed (the stable version was only added after the switch to LP64D).
Conversely, BR2_TOOLCHAIN_EXTERNAL_BOOTLIN_RISCV64_MUSL_BLEEDING_EDGE,
which was removed, was not mentioned in Config.in.legacy.
Correct the symbol name and its comment in Config.in.legacy.
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>