projects/RPi: switch to kernel 3.16

Signed-off-by: Stephan Raue <stephan@openelec.tv>
linux: remove kernel 3.15 support

Signed-off-by: Stephan Raue <stephan@openelec.tv>
libressl: update to libressl-2.0.4

Signed-off-by: Stephan Raue <stephan@openelec.tv>