x86: merge some trivially mergeable headers

Merge errno.h, resource.h, rtc.h, sections.h, serial.h and sockios.h,
where i386 and x86_64 have no or only trivial comment/include guard
differences.

Build tested on both 32-bit and 64-bit, and booted on 64-bit.

[tglx: fixup Kbuild as well]

Signed-off-by: Roland Dreier <roland@digitalvampire.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>