i2c, davinci: move i2c_defs.h to the drivers/i2c directory

This patch moves the davinci i2c_defs.h file to drivers.i2c directory.
It will allow to reuse the davinci_i2c driver for TI Keystone2 SOCs.

Not used "git mv" command to move the file because small part of
it with definitions specific for Davinci SOCs has to remain in the
arch/arm/include/asm/arch-davinci.

Signed-off-by: Vitaly Andrianov <vitalya@ti.com>
Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>
Acked-by: Tom Rini <trini@ti.com>