Ovidiu Panait authored Feb 05, 2020 and Tom Rini committed Feb 13, 2020

clear_bss is already used by 3 arches (x86, arc, xtensa), so make it generic
and provide a weak nop stub for it. This also removes arch-specific ifdef
duplications around clear_bss.

Signed-off-by: Ovidiu Panait <ovpanait@gmail.com>