Handle the manufacturer, device and version IDs separately rather than
smooshing them all together into a single uint32_t. Note that the ID
registers are actually 16 bit, even though typically the top bits are 0
and the Read Identification Data command only returns the bottom 8 bits.

Signed-off-by: Juha Riihimäki <juha.riihimaki@nokia.com>
[Riku Voipio: Fixes and restructuring patchset]
Signed-off-by: Riku Voipio <riku.voipio@iki.fi>
[Peter Maydell: More fixes and cleanups for upstream submission]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Andrzej Zaborowski <andrew.zaborowski@intel.com>