hw/char/pl011: Remove duplicated PL011_INT_[RT]X definitions

PL011_INT_TX duplicates INT_TX, and PL011_INT_RX INT_RX.
Follow other register fields definitions from this file,
keep the shorter form.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20230522153144.30610-6-philmd@linaro.org>