bios-tables-test: Make oem-fields tests be consistent

bios-tables-test: Make oem-fields tests be consistent

Every other test function is named:

	test_acpi_<machine>_<test>()

Just make this test the same.  Once there, rename "acpi/oem-fields" to
"acpi/piix4/oem-fields" so it is consistent with everything else.

Signed-off-by: Juan Quintela <quintela@redhat.com>
Message-Id: <20220902173452.1904-2-quintela@redhat.com>
Reviewed-by: Ani Sinha <ani@anisinha.ca>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>