This patch adds an inline function in_module() to check which space the
instruction pointer in, kernel space or module space.
Note: This will not work when the kernel space and module space are the
same. If they are the same, we need to modify scripts/recordmcount.pl,
ftrace_make_nop/call() and the other related parts to ensure the
enabling/disabling of the calling site to _mcount is right for both
kernel and module.
[Ralf: It also is still incorrect for some 64-bit kernels.]