add generic fixmap.h

add generic fixmap.h

Many architectures provide an asm/fixmap.h which defines support for
compile-time 'special' virtual mappings which need to be made before
paging_init() has run.  This support is also used for early ioremap on
x86.  Much of this support is identical across the architectures.  This
patch consolidates all of the common bits into asm-generic/fixmap.h
which is intended to be included from arch/*/include/asm/fixmap.h.

Signed-off-by: Mark Salter <[email protected]>
Acked-by: Arnd Bergmann <[email protected]>
Acked-by: Ralf Baechle <[email protected]>
Cc: Russell King <[email protected]>
Cc: Richard Kuo <[email protected]>
Cc: James Hogan <[email protected]>
Cc: Michal Simek <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Chris Metcalf <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Jeff Dike <[email protected]>
Cc: Paul Mundt <[email protected]>
Cc: Richard Weinberger <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Jonas Bonn <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>