.gitignore for generated files in api_examples directory

Add .gitignore for generated files in api_examples directory

Signed-off-by: Jon Smirl <jonsmirl@gmail.com>
Signed-off-by: Wolfgang Denk <wd@denx.de>

api_examples/.gitignore

+crc32.c
+ctype.c
+demo
+demo.bin
+ppcstring.S
+string.c
+vsprintf.c