target/sparc: Fix ARRAY8

Follow the Oracle Sparc 2015 implementation note and bound
the input value of N to 5 from the lower 3 bits of rs2.
Spell out all of the intermediate values, matching the diagram
in the manual.  Fix extraction of upper_x and upper_y for N=0.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
1 file changed