bindings: perf: imx-ddr: add compatible string

Add extra compabile string to support driver.

Signed-off-by: Joakim Zhang <qiangqing.zhang@nxp.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20201130114202.26057-2-qiangqing.zhang@nxp.com


Signed-off-by: Will Deacon <will@kernel.org>