coresight: etm4x: Use asm-generic IO memory barriers

Per discussion in [1], it was decided to move to using architecture
independent/asm-generic IO memory barriers to have just one set of
them and deprecate use of arm64 specific IO memory barriers in driver
code. So replace current usage of __io_rmb()/__iowmb() in drivers to
__io_ar()/__io_bw().

[1] https://lore.kernel.org/lkml/CAK8P3a0L2tLeF1Q0+0ijUxhGNaw+Z0fyPC1oW6_ELQfn0=i4iw@mail.gmail.com/

Signed-off-by: Sai Prakash Ranjan <quic_saipraka@quicinc.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>