hw/arm/xen_arm.c: convert DPRINTF to trace events and error/warn reports

hw/arm/xen_arm.c: convert DPRINTF to trace events and error/warn reports

Tracing DPRINTFs to stderr might not be desired. A developer that relies
on trace events should be able to opt-in to each trace event and rely on
QEMU's log redirection, instead of stderr by default.

This commit converts DPRINTFs in this file that are used for tracing
into trace events. Errors or warnings are converted to error_report and
warn_report calls.

Signed-off-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-id: fe5e3bd54231abe933f95a24e0e88208cd8cfd8f.1706544115.git.manos.pitsidianakis@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>