Each disk device has its own id now. This is useful to make use
of multiple disk devices.
* include/grub/disk.h (grub_disk_dev_id): New enum.
(GRUB_DISK_DEVICE_BIOSDISK_ID): New constant.
(GRUB_DISK_DEVICE_OFDISK_ID): Likewise.
* disk/i386/pc/biosdisk.c (grub_biosdisk_dev): Specify
GRUB_DISK_DEVICE_BIOSDISK_ID as an id.
* disk/powerpc/ieee1275/ofdisk.c (grub_ofdisk_dev): Specify
GRUB_DISK_DEVICE_OFDISK_ID as an id.
* util/i386/pc/biosdisk.c (grub_util_biosdisk_dev): Specify
GRUB_DISK_DEVICE_BIOSDISK_ID as an id.
* include/grub/disk.h (struct grub_disk_dev): Added a new member
"id" which is used by the cache manager.
* normal/main.c (grub_normal_init_page): Use "GNU GRUB" instead
of just "GRUB".