davinci: Support JTAG ID register at any address

The Davinci cpu_is_davinci_*() macros use the SoC part number
and variant retrieved from the JTAG ID register to determine the
type of cpu that the kernel is running on.  Currently, the code to
read the JTAG ID register assumes that the register is always at
the same base address.  This isn't true on some newer SoCs.

To solve this, have the SoC-specific code set the JTAG ID register
base address in soc_info structure and add a 'cpu_id' member to it.
'cpu_id' will be used by the cpu_is_davinci_*() macros to match
the cpu id.  Also move the info used to identify the cpu type into
the SoC-specific code to keep all SoC-specific code together.

The common code will read the JTAG ID register, search through
an array of davinci_id structures to identify the cpu type.
Once identified, it will set the 'cpu_id' member of the soc_info
structure to the proper value and the cpu_is_davinci_*() macros
will now work.

Signed-off-by: Mark A. Greer <mgreer@mvista.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>