ide: add IDE_HFLAG_BOOTABLE host flag

Add IDE_HFLAG_BOOTABLE host flag and IDE_HFLAG_OFF_BOARD define.  Convert
all host drivers using ide_pci_device_t to use IDE_HFLAG_{BOOTABLE,OFF_BOARD}
instead of d->bootable and then remove no longer needed d->bootable.

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
diff --git a/drivers/ide/pci/triflex.c b/drivers/ide/pci/triflex.c
index 68e1e9a..8f89b6d 100644
--- a/drivers/ide/pci/triflex.c
+++ b/drivers/ide/pci/triflex.c
@@ -113,7 +113,7 @@
 	.init_hwif	= init_hwif_triflex,
 	.autodma	= AUTODMA,
 	.enablebits	= {{0x80, 0x01, 0x01}, {0x80, 0x02, 0x02}},
-	.bootable	= ON_BOARD,
+	.host_flags	= IDE_HFLAG_BOOTABLE,
 	.pio_mask	= ATA_PIO4,
 };