x86: i387 renaming

This renames arch/x86/kernel/{i387_32.c => i387.c}.
This is a pure renaming, but paves the way for merging
the 32-bit and 64-bit versions of this code.

Signed-off-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>