linux: Add sparck brk implementation

It turned that the generic implementation of brk() does not work
for sparc, since on failure kernel will just return the previous
input value without setting the conditional register.

This patches adds back a sparc32 and sparc64 implementation removed
by 72048093.

Checked on sparc64-linux-gnu and sparcv9-linux-gnu.

(cherry picked from commit 5b86241a)