gpiolib: allow user-selection

gpiolib: allow user-selection

This patch adds functionality to the gpio-lib subsystem to make it
possible to enable the gpio-lib code even if the architecture code didn't
request to get it built in.

The archtitecture code does still need to implement the gpiolib accessor
functions in its asm/gpio.h file.  This patch adds the implementations for
x86 and PPC.

With these changes it is possible to run generic GPIO expansion cards on
every architecture that implements the trivial wrapper functions.  Support
for more architectures can easily be added.

Signed-off-by: Michael Buesch <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Stephen Rothwell <[email protected]>
Cc: David Brownell <[email protected]>
Cc: Russell King <[email protected]>
Cc: Haavard Skinnemoen <[email protected]>
Cc: Jesper Nilsson <[email protected]>
Cc: Ralf Baechle <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Jean Delvare <[email protected]>
Cc: Samuel Ortiz <[email protected]>
Cc: Kumar Gala <[email protected]>
Cc: Sam Ravnborg <[email protected]>
Cc: Adrian Bunk <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>