asm-generic: Import functions from Linux

Currently {read,write}s{b,w,lq}() functions are available only on some
architectures, and there are no io{read,write}{8,16,32,64}_rep()
functions in u-boot. This patch adds generic versions that may be used
without arch-specific implementation.

Since some of added functions were already added locally in some files,
remove them to avoid redeclaration errors.

Signed-off-by: Igor Prusov <ivprusov@salutedevices.com>