extable: Make init_kernel_text() global

extable: Make init_kernel_text() global

Convert init_kernel_text() to a global function and use it in a few
places instead of manually comparing _sinittext and _einittext.

Note that kallsyms.h has a very similar function called
is_kernel_inittext(), but its end check is inclusive.  I'm not sure
whether that's intentional behavior, so I didn't touch it.

Suggested-by: Jason Baron <[email protected]>
Signed-off-by: Josh Poimboeuf <[email protected]>
Acked-by: Peter Zijlstra <[email protected]>
Acked-by: Steven Rostedt (VMware) <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Link: http://lkml.kernel.org/r/4335d02be8d45ca7d265d2f174251d0b7ee6c5fd.1519051220.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <[email protected]>