This replaces a static array with 8 bytes per register. When there are
vector registers larger than 8 bytes, they would end up clobbering each
other's values. I can't believe I didn't catch this earlier.
Change-Id: I9df4eaf05617a2c8df3140fff9fe53f61ab2b261
Signed-off-by: Tim Newsome <tim@sifive.com>