i2c-pnx: Fix interrupt handler, get rid of EARLY config option

This fixes two issues raised by David Brownell on the i2c list:

<< Someone needs to update i2c-pnx.c to handle the IRQ handler doesn't
expect pt_regs (gone now for a while), and so it doesn't try to
reference "mudule_init()" if I2C isn't initialized "early".  For
that matter, to get rid of that _option_ to initialize then, and
always init that driver with subsystem_init() ... it's common with
embedded systems to need I2C access to tweak a GPIO expander or
do some other work when bringing up drivers, that's not specific
to USB stacks. >>

Signed-off-by: Vitaly Wool <vitalywool@gmail.com>
Signed-off-by: Jean Delvare <khali@linux-fr.org>