nanokernel: move dataCopy() and bssZero() to common code

Used by ARC, ARM, Nios II. x86 has alternate code done in assembly.

Linker scripts had some alarming comments about data/BSS overlap,
but the beginning of BSS is aligned so this can't happen even if
the end of data isn't.

The common code doesn't use fake pointer values for the number of
words in these sections, don't compute or export them.

Change-Id: I4291c2a6d0222d0a3e95c140deae7539ebab3cc3
Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>