sparc64-8bit-asi

sparc64-8bit-asi

Sparc64 alternate space load/store helpers expect 8 bit ASI value,
while wrasi implementation sign-extends ASI operand causing
for example 0x80 to appear as 0xFFFFFF80. Resulting value falls
out of switch in helpers and causes obscure load/store faults.

- correct wrasi by masking lower 8 bits of xor result
- use lower 8 bits of ASI register in helpers

Signed-off-by: Igor V. Kovalenko <igor.v.kovalenko@gmail.com>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>