fs: rename inode member of struct filep to priv ...

Because that's what it is. 'inode' will become confusing
once we support real inodes.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

fs: implement EFI filesystem driver ...

This implements a filesystem driver which uses the EFI Simple File
System Protocol to provide files from EFI to barebox.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>