msm: adsprpc: use persistent header buffers

Add IOCTL support for userspace to request kernel to enable
optimizations to reduce RPC overhead. This change specifically
enables the use of persistent header buffers, allocated during
process setup time and mapped on DSP in one call. Try using
persistent headers for RPC calls and fall back to allocating a new
buffer if all buffers are in use already.

Change-Id: If106679947adfaabb08055f3ad909711bc891656
Acked-by: Thyagarajan Venkatanarayanan <venkatan@qti.qualcomm.com>
Signed-off-by: Himateja Reddy <hmreddy@codeaurora.org>