mini-os: create app-specific configuration

mini-os: create app-specific configuration

Instead of using CONFIG_QEMU and CONFIG_GRUB to enable or disable minios
code, create CONFIG_ items for features and use application-specific
configuration files to enable or disable the features.

The configuration flags are currently added to the compiler command
line; as the number of flags grows this may need to move to a header.

Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Committed-by: Ian Jackson <Ian.Jackson@eu.citrix.com>