msm: adsprpc: remove DMA coherency attributes in fastrpc driver

Remove the use of DMA_ATTR_FORCE_NON_COHERENT and
DMA_ATTR_FORCE_COHERENT attributes while allocating and mapping
memory in the fastrpc driver, as they are not supported in a GKI
kernel. Ignore any per-buffer coherency attributes passed by
userspace.

Add a new config option that can be used by the fastrpc driver to
detect if it is being compiled in a QGKI kernel. Read the DMA
coherency property of the fastrpc device nodes only if this config
has been enabled. On a GKI kernel, the cache maintenance will
always be done by the fastrpc driver.

Change-Id: Id1e715da4462d9fb8819fc1c85f7b0c7d8610f24
Acked-by: Thyagarajan Venkatanarayanan <venkatan@qti.qualcomm.com>
Signed-off-by: Himateja Reddy <hmreddy@codeaurora.org>