target/arm: Convert BRAA, BRAB, BLRAA, BLRAB to decodetree

target/arm: Convert BRAA, BRAB, BLRAA, BLRAB to decodetree

Convert the last four BR-with-pointer-auth insns to decodetree.
The remaining cases in the outer switch in disas_uncond_b_reg()
all return early rather than leaving the case statement, so we
can delete the now-unused code at the end of that function.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20230512144106.3608981-20-peter.maydell@linaro.org