target/arm: Use acpi_ghes_present() to see if we report ACPI memory errors

target/arm: Use acpi_ghes_present() to see if we report ACPI memory errors

The virt_is_acpi_enabled() function is specific to the virt board, as
is the check for its 'ras' property.  Use the new acpi_ghes_present()
function to check whether we should report memory errors via
acpi_ghes_record_errors().

This avoids a link error if QEMU was built without support for the
virt board, and provides a mechanism that can be used by any future
board models that want to add ACPI memory error reporting support
(they only need to call acpi_ghes_add_fw_cfg()).

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Dongjiu Geng <gengdongjiu1@gmail.com>
Message-id: 20210603171259.27962-4-peter.maydell@linaro.org