Changeset 258 for soft/giet_vm/giet_drivers

This is a major release, including a deep restructuration of code.
The main evolutions are

• use of the Tsar preloader to load the GIET boot-loader from disk
• introduction of a FAT32 file system library,
• use of this fat32 library by the boot-loader to load the map.bin data structure, and the various .elf files
• reorganisation of drivers (one file per peripheral).
• introduction of drivers for new peripherals: vci_chbuf_dma and vci_multi_ahci.
• introduction of a new physical memory allocator in the boot code.

This release has been tested on the tsar_generic_iob architecture,
for the two following mappings: 4c_1p_iob_four.xml and 4c_1p_iob_sort.xml