[top_earlgrey_verilator] Use faster build options
[top_earlgrey_verilator] Use faster build options

Verilator improved its default options compile options a lot in the
past, now giving much better and performant defaults than before. Remove
custom options to let these new defaults take effect.

With this change, on my machine, the build time on my machine is reduced
from 6:30 min to 1:21 min.

Signed-off-by: Philipp Wagner <5a4b10454c30419e54a1570be358a516ff84bb63@lowrisc.org>

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