debuggerd: Fix missing include.

The structure user_vfp is incorrectly defined in bionic/libc/kernel/arch-arm/asm/ptrace.h
at the moment, while it should be under bionic/libc/kernel/arch-arm/asm/user.h instead.

Before moving its definition in the corresponding source files, we need to fix its users.
It happens that debuggerd is the only one for now, so fix this by including <linux/user.h>
instead (which will include <asm/user.h> and <asm/ptrace.h>).

Also, make the debug output less chatty by specifying all symbols to be listed
through XLOG2 instead of XLOG.

Change-Id: I16e0fa700945d86efd44ee885a84ad609c0a9b58