Improve __copy_to_user and __copy_from_user performance

Provide a __copy_from_user that uses memcpy. On BCM2708, use
optimised memcpy/memmove/memcmp/memset implementations.
bcm2708: Eliminate i2s debugfs directory error

Qualify the two regmap ranges uses by bcm2708-i2s ('-i2s' and '-clk')
to avoid the name clash when registering debugfs entries.