phy: amlogic: meson8b-usb2: Add a compatible string for Meson8m2

The 3.10 vendor kernel sets the ACA_ENABLE bit on Meson8b, Meson8m2 and
GXBB, but not on Meson8. Add a compatible string for Meson8m2 which also
sets that bit.
While here, also update the Kconfig text and MODULE_DESCRIPTION.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Tested-by: Thomas Graichen <thomas.graichen@gmail.com>
Link: https://lore.kernel.org/r/20200512222424.549351-7-martin.blumenstingl@googlemail.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>