Add .gitignore

Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>
makefile: add cscope target

Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>
makefile: use Android environment variables to locate cross compiler and kernel sources

This makes it more flexible to compile with different Android trees and products.

Instead of using hardcoded ROOT_PATH variable use ARM_EABI_TOOLCHAIN and ANDROID_PRODUCT_OUT which
is set by breakfast in CM.

Also update README.

Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>
makefile: make it possible to set/override android variables in .config

In case someone doesn't want to run breakfast or other build scripts the paths can be hardcoded
in .config file.

Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>