target-xtensa: add basic checks to dcache opcodes Check privilege level for privileged instructions (DHI, DHU, DII, DIU, DIWB, DIWBI, DPFL are privileged), memory accessibility for instructions that reference memory (all DH* and DPFL) and windowed register validity for all data cache instructions. Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>