support/config-fragments/autobuild: fix bootlin-riscv64 configs

commit b3c66481 replaced RISC-V LP64
bootlin toolchains by RISC-V LP64D. The config symbols
BR2_TOOLCHAIN_EXTERNAL_BOOTLIN_RISCV64_GLIBC_BLEEDING_EDGE and
BR2_TOOLCHAIN_EXTERNAL_BOOTLIN_RISCV64_GLIBC_STABLE were marked as legacy.
Those changes were not reflected in the autobuild toolchain configs in
support/config-fragments/autobuild/bootlin-riscv64-{glibc,musl}.config

When testing a package with the command:

    ./utils/test-pkg --all --package somepackage

bootlin-riscv64-{glibc,musl} toolchain are always skipped. The build
logfile contains:

    [...]
    Value requested for BR2_TOOLCHAIN_EXTERNAL_BOOTLIN not in final .config
    Requested value:  BR2_TOOLCHAIN_EXTERNAL_BOOTLIN=y
    Actual value:

    Value requested for BR2_TOOLCHAIN_EXTERNAL_BOOTLIN_RISCV64_GLIBC_BLEEDING_EDGE not in final .config
    Requested value:  BR2_TOOLCHAIN_EXTERNAL_BOOTLIN_RISCV64_GLIBC_BLEEDING_EDGE=y
    Actual value:     # BR2_TOOLCHAIN_EXTERNAL_BOOTLIN_RISCV64_GLIBC_BLEEDING_EDGE is not set

This commit update the autobuild config fragments for RISC-V 64bit
toolchains so they can be used by test-pkg.

Signed-off-by: Julien Olivain <ju.o@free.fr>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>