bblayers.conf.sample: Add meta-riscv

Add meta-riscv to bblayers.conf.sample to enable RISC-V support
in all ASOS builds

Signed-off-by: Bernhard Rosenkränzer <bernhard.rosenkraenzer.ext@huawei.com>

flavours/linux/bblayers.conf.sample

@@ -36,4 +36,5 @@ BBLAYERS ?= " \
   ##OEROOT##/../meta-raspberrypi \
   ##OEROOT##/../meta-security \
   ##OEROOT##/../meta-linaro/meta-optee \
+  ##OEROOT##/../meta-riscv \
   "