"improve" rather than "fix" as `pstate.0x3` is hardly as useful as
`msr uao, #3`. but the "pstate field" that had been decoded before was
totally incorrect.

Correct the shift used to select condition bits and correctly compute the
branch offset.

Sign extension shift had an off-by-one error so the sign bit was not being
properly extended.

T4 encodings of unconditional branches were not being interpreted correctly
(#6), and 32-bit bl/blx instructions were similarly incorrect. Correct the bits
selected for op1 and op2 and handle the slightly-unusual i1/i2 sign bit xor for
these instructions.