mfd: TWL5030 version checking in twl-core

Added API to get the TWL5030 Si version from the IDCODE register.
It is used for enabling the workaround for TWL erratum 27.

Signed-off-by: Lesly A M <leslyam@ti.com>
Cc: Nishanth Menon <nm@ti.com>
Cc: David Derrick <dderrick@ti.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>