i2c-i801: Use the internal 32-byte buffer on ICH4+

Add an ability to utilize the internal SRAM buffer on ICH4
and newer host controllers to speed up execution of block operations.

I've split the code so that it is more clear which block transaction is
performed.

First of all the host controller's type is identified. isich4 is set when
we think that the controller has the internal buffer. Then, before every
block transaction, if isich4 is set, we attempt to enable the E32B bit in
SMBAUXCTL register.

Signed-off-by: Oleg Ryjkov <olegr@google.com>
Signed-off-by: Jean Delvare <khali@linux-fr.org>