Hexagon: fix build errors

Fix type-o in ptrace.c.
Add missing include: asm/hexagon_vm.h
Remove superfluous cast.
Replace 'p3_0' with 'preds'.

Signed-off-by: Sid Manning <sidneym@codeaurora.org>
Add -mlong-calls to build flags.
Signed-off-by: Brian Cain <bcain@codeaurora.org>

Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>