add uEnv.txt for custom boot

olinux/uEnv.txt

@@ -0,0 +1,11 @@
+baudrate=115200
+console=ttyS0,115200
+bootdelay=1
+bootenv=uEnv.txt
+bootscr=boot.scr
+kernel=uImage
+loglevel=8
+panicarg=panic=10
+root=/dev/mmcblk0p2 rootwait
+extraargs=sunxi_ve_mem_reserve=0 sunxi_no_mali_mem_reserve sunxi_g2d_mem_reserve=0 sunxi_fb_mem_reserve=8 
+setargs=setenv bootargs console=${console} root=${root} loglevel=${loglevel} ${panicarg} ${extraargs}