x86/boot: Move EISA setup to a separate file

EISA has absolutely nothing to do with traps, so move it out of traps.c
into its own eisa.c file.

Furthermore, the EISA bus detection does not need to run during
very early boot, it's good enough to run it before the EISA bus
and drivers are initialized.

I.e. instead of calling it from the very early trap_init() code,
make it a subsys_initcall().

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/20170828064956.515322409@linutronix.de


Signed-off-by: Ingo Molnar <mingo@kernel.org>