top: Improve 'clean' and 'distclean' makefile targets

This improves 'clean' and 'distclean' makefile target as follows:
1. Remove only .o, .a, .elf, and .bin files for 'clean'
2. Remove .dep in-addition to what 'clean' does for 'distclean'
3. Remove default build and install directory for 'distclean'

Signed-off-by: Anup Patel <anup.patel@wdc.com>