ide-disk: move /proc handling to ide-disk_proc.c (take 3)

While at it:
- idedisk_capacity() -> ide_disk_capacity()
- idedisk_proc[] -> ide_disk_proc[]
- idedisk_settings[] -> ide_disk_settings[]

v2/3:
Build fix for CONFIG_IDE_PROC_FS=n from Elias Oltmanns.

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>

drivers/ide/ide-disk.h

@@ -13,6 +13,7 @@ struct ide_disk_obj {
 	container_of((disk)->private_data, struct ide_disk_obj, driver)
 
 /* ide-disk.c */
+sector_t ide_disk_capacity(ide_drive_t *);
 ide_decl_devset(address);
 ide_decl_devset(multcount);
 ide_decl_devset(nowerr);
@@ -22,4 +23,10 @@ ide_decl_devset(acoustic);
 /* ide-disk_ioctl.c */
 int ide_disk_ioctl(struct inode *, struct file *, unsigned int, unsigned long);
 
+#ifdef CONFIG_IDE_PROC_FS
+/* ide-disk_proc.c */
+extern ide_proc_entry_t ide_disk_proc[];
+extern const struct ide_proc_devset ide_disk_settings[];
+#endif
+
 #endif /* __IDE_DISK_H */