boot: add s500-bootloader package

boot: add s500-bootloader package

This is the first level bootloader for the Actions Semiconductor S500 SoC,
which is used on boards like Roseapple Pi and LeMaker Guitar.

The bootloader performs basic configuration and chain loads u-boot for
futher setup.

This bootloader is unfortunately only available as a binary blob. It gets
configured for a specific board using a binary (32bit x86) tool based on a
.ini file (somewhat similar to sunxi .fex).

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>