sl82c105: rework PIO support (take 2)

Get rid of the 'pio_speed' member of 'ide_drive_t' that was only used by this
driver by storing the PIO mode timings in the 'drive_data' instead -- this
allows us to greatly  simplify the process of "reloading" of the chip's timing
register and do it right in sl82c150_dma_off_quietly() and to get rid of two
extra arguments to config_for_pio() -- which got renamed to sl82c105_tune_pio()
and now returns a PIO mode selected, with ide_config_drive_speed() call moved
into the tuneproc() method, now called sl82c105_tune_drive() with the code to
set drive's 'io_32bit' and 'unmask' flags in its turn moved to its proper place
in the init_hwif() method.
Also, while at it, rename get_timing_sl82c105() into get_pio_timings() and get
rid of the code in it clamping cycle counts to 32 which was both incorrect and
never executed anyway...

Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>

include/linux/ide.h

@@ -613,7 +613,6 @@ typedef struct ide_drive_s {
 
         u8	quirk_list;	/* considered quirky, set for a specific host */
         u8	init_speed;	/* transfer rate set at boot */
-        u8	pio_speed;      /* unused by core, used by some drivers for fallback from DMA */
         u8	current_speed;	/* current transfer rate set */
 	u8	desired_speed;	/* desired transfer rate set */
         u8	dn;		/* now wide spread use */