Add .gitignore files

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Acked-by: Kim Phillips <kim.phillips@freescale.com>

.gitignore

+*.orig
+*.a
+*.o
+*.depend
+System.map
+/u-boot
+/u-boot.map
+/u-boot.bin
+/u-boot.srec
+/LOG
+/errlog
+/reloc_off
+

examples/.gitignore

+/hello_world
+/interrupt
+/sched
+*.bin
+*.srec

include/.gitignore

+/asm
+/asm-ppc/arch
+/bmp_logo.h
+/config.h
+/config.mk
+/version_autogenerated.h

tools/.gitignore

+/bmp_logo
+/crc32.c
+/envcrc
+/environment.c
+/gen_eth_addr
+/img2srec
+/mkimage
+/sha1.c
+/ubsha1