fsl_pq_mdio: Fix iomem unmapping for non-eTSEC2.0 controllers

fsl_pq_mdio: Fix iomem unmapping for non-eTSEC2.0 controllers

We use a rather complicated logic to support eTSEC and eTSEC2.0
registers maps in a single driver. Currently, the code tries to
unmap 'regs', but for non-eTSEC2.0 controllers 'regs' doesn't
point to a mapping start, and this might cause badness on probe
failure or module removal:

 Freescale PowerQUICC MII Bus: probed
 Trying to vfree() nonexistent vm area (e107f000)
 ------------[ cut here ]------------
 Badness at c00a7754 [verbose debug info unavailable]
 NIP: c00a7754 LR: c00a7754 CTR: c02231ec
 [...]
 NIP [c00a7754] __vunmap+0xec/0xf4
 LR [c00a7754] __vunmap+0xec/0xf4
 Call Trace:
 [df827e50] [c00a7754] __vunmap+0xec/0xf4 (unreliable)
 [df827e70] [c001519c] iounmap+0x44/0x54
 [df827e80] [c028b924] fsl_pq_mdio_probe+0x1cc/0x2fc
 [df827eb0] [c02fb9b4] of_platform_device_probe+0x5c/0x84
 [df827ed0] [c0229928] really_probe+0x78/0x1a8
 [df827ef0] [c0229b20] __driver_attach+0xa4/0xa8

Fix this by introducing a proper priv structure (finally!), which
now holds 'regs' and 'map' fields separately.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: David S. Miller <davem@davemloft.net>