[RFC] Introduce __ARCH_WANT_SYS_SYSFS

[Will Newton]

 Hi,

This patch introduces a __ARCH_WANT_SYS_SYSFS #define for
architectures that support the sysfs(2) system call. At the moment
that's everybody but blackfin, but future architectures may want to
save the (admittedly small) code size that it adds to the kernel as
well.

(patch attached as well as inline because gmail seems to mangle my whitespace)

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