[RISCV] Rework .option arch target streamer interface

The current interface requires some rather ugly tracking of state due to
splitting up the calls for each argument. Instead, pack them all into a
single call by passing an ArrayRef. Also clean up the dodgy whitespace
emitted for the directive whilst here; there was a stray space between
the tab and .option, and there was a tab rather than a space after the
first comma for some strange reason.

Reviewed By: craig.topper

Differential Revision: https://reviews.llvm.org/D152193