msm: cvp: Avoid overflowing the stack frame

Building with llvm generates the following warning:

  drivers/media/platform/msm/cvp//msm_cvp_ioctl.c:611:13: warning: stack frame
  size of 2064 bytes in function 'cvp_ioctl' [-Wframe-larger-than=]

struct cvp_kmd_hfi_packet is 1880 bytes and is a member of a union inside
struct cvp_kmd_arg which eventually triggers the warning. Allocate the
struct from the heap instead.

Fixes: ffe925cb ("msm: cvp: Port CVP driver to 5.x kernel")
Change-Id: Ic0dedbad82d36b7faade85c3428b1013b527b576
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>