flavours: add meta-rauc to the Linux flavour

SystemOTA depends on RAUC. The meta-rauc repository was added to the
manifest earlier [1], and now needs to participate in the default build
configuration process.

[1] https://git.ostc-eu.org/OSTC/OHOS/manifest/-/merge_requests/127



Signed-off-by: Zygmunt Krynicki <zygmunt.krynicki@huawei.com>