Merged composite syscall entry into the main syscall entry.
Moved sysenter entry into C file as inline asm. Unfortunately gcc
doesn't locate the functions as I expected -- sysenter_entry and
dispatcher functions are not in the same page. Going to solve this.
Ensured sysenter_interposition and sysenter_handler are located in the
same page (by allocating a new ipc_entry section).
Removed the sysenter_interposition inline asm in ipc.h, since that
didn't help us. We still have the asm entry in kern_entry.S in
__ipc_entry section, same as the sysenter_handler in C.