fastrpc : fastrpc porting for kernel 4.19 SPF targets

changes in fastrpc for porting kernel to 4.19.

Change-Id: I19bfa21914e6c6cb9c4c6e1c4c9a75bdb0594381
Signed-off-by: Akhil Manikoth Kallankandy <akhika@codeaurora.org>