target/i386: Cleanup read_crN, write_crN, lmsw

target/i386: Cleanup read_crN, write_crN, lmsw

Pull the svm intercept check into the translator.
Pull the entire implementation of lmsw into the translator.
Push the check for CR8LEG into the regno validation switch.
Unify the gen_io_start check between read/write.

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20210514151342.384376-40-richard.henderson@linaro.org>