x86: correctly set UTS_MACHINE for "make ARCH=x86"

For a kernel built with "make ARCH=x86" the following system
information is displayed when running the new kernel

    $ uname -m
    x86

On some i386 systems (e.g. K7) we even have the following information

    $ uname -m
    x66

This is weird. The usual information for "uname -m" should be "x86_64"
on 64-bit and "i386" or "i686" on 32-bit.

This patch fixes the issue by setting UTS_MACHINE to "i386" for 32-bit
kernel builds and to "x86_64" for 64-bit kernel builds. I.e., "x86"
won't be used for UTS_MACHINE anymore.
Acked-by: NSam Ravnborg <sam@ravnborg.org>
Signed-off-by: NAndreas Herrmann <aherrman@arcor.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Roman Zippel <zippel@linux-m68k.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@redhat.com>

For x86 ARCH may say i386 or x86_64 and soon x86.
Rely on CONFIG_X64_32 to select between 32/64 or just
hardcode the value as appropriate.
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>

With some small changes to kconfig makefile we can now
locate the defconfig files for i386 and x86_64 in
the configs/ subdirectory under x86.
make ARCH=i386 defconfig and make defconfig
works as expected also after this change.
But arch maintainers shall now update a defconfig file in
the configs/ directory.
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>

Moving the ARCH specific Makefiles for i386 and x86_64
required a litle bit tweaking in the top-lvel Makefile.

SRCARCH is now set in the top-level Makefile
because we need this info to include the correct
arch Makefile.
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>