kernel: replace .BSS and .DATA setup with standard library calls

Use standard library calls like memset/memcpy for setting up BSS and DATA
sections during system initialization, this helps to take advantage of
architecture specific optimizations from standard library.

Change-Id: Ia72b42aa65b44d1df7c22dd1fbc39a44fa001be9
Signed-off-by: Mahavir Jain <mjain@marvell.com>