Fix and shorten BERI kernel builds during universe.

Stop building BERI_DE4_BASE and BERI_SIM_BASE, they aren't particularly
valid as they don't have a root dev. Do build BERI_DE4_SDROOT which
does so devices get coverage.

Remove ident from BERI_DE4_BASE for the reasons above which will cause
it to fail to build. BERI_SIM_BASE was already this way and broke
universe.[0]

Reported by: rpokala
Sponsored by: DARPA, AFRL