Evaluate functions inside sw-description
Evaluate functions inside sw-description

Instead to add new rules to parse sw-description to generate data,
create a generic method to let the class to call a function. It is then
enough to create a list / libraries of these function instead to find
new ways to extend sw-description's syntax.

Signed-off-by: Stefano Babic <2c2905e0c2877c7e4ce40c7425e972302953fda5@denx.de>

sbabic/meta-swupdate,sbabic/meta-swupdate