config: change CONFIG_DMATEST from y to m

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I59Q07


CVE: NA

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Simple DMA test client. Say N unless you're debugging a DMA Device driver.
It doesn't need to be compiled into the vmlinux, change it to m.

Signed-off-by: Chao Liu <liuchao173@huawei.com>
Reviewed-by: Kai Liu <kai.liu@suse.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>