firmware: qcom_scm: Set DMA coherent mask as well as the streaming mask

The driver currently sets up the DMA streaming mask to
64 bits, which helps with being able to map memory above 32 bits
with the DMA APIs. However, when allocating coherent memory,
the DMA framework will allocate memory, and ensure that the memory
is within the device's coherent memory limitations, not the streaming
limitations. Since the coherent DMA mask is not set up for the device,
it is left at its default value--32 bits--so any allocations that have
an address above 32 bits will be deemed as not suitable to satisfy the
allocation.

There is no limitation for coherent memory access for the SCM device,
so align it to the 64 bit streaming DMA mask.

Change-Id: I5a8493ec31e06aa6a80e4fab31bce1fc6e13fbf3
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>