serial: amba-pl011: Enable UART in earlycon setup

serial: amba-pl011: Enable UART in earlycon setup

Currently the PL011 driver only enables the UART (by setting UARTEN
in REG_CR) in pl011_startup(), so if it is used for earlycon it is
relying on the bootrom/firmware having left the UART enabled.

There's no particular reason not to actively enable the UART before
using it for earlycon, and the earlycon handling for e.g. the 8250
UART sets up the UART in its setup function, so follow that in the
PL011.

This allows use of earlycon with a UART that the firmware hasn't
already been using for its own output, but the main motivation is
that QEMU will otherwise log a message complaining that the guest is
trying to write to a UART it never enabled.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Link: https://patch.msgid.link/20260210125100.223138-1-peter.maydell@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>