tcg: Standardize on TCGReg as the enum for hard registers

tcg: Standardize on TCGReg as the enum for hard registers

Most targets did not name the enum; tci used TCGRegister.

Signed-off-by: Richard Henderson <rth@twiddle.net>
Reviewed-by: Andreas Färber <afaerber@suse.de>
Reviewed-by: Stefan Weil <sw@weilnetz.de>
Signed-off-by: Alexander Graf <agraf@suse.de>