Fixed I2C bug

Modified the register settings of communication frequency .
Fix a unreadable comments.

There were some Japanese comments in I2C source code.
Fixed those comments to be readable.
Implement peripheral clock determination process to I2C driver

When making I2C communication freq, we used a fix value 33.3MHz as peripheral clock as below.
   pclk = 33333333 / (2 << count);

But it is not dynamic when system clock is changed.
So, implement peripheral clock determination process.
Peripheral clock will be decided by RZ-A1H system clock mode.
Merge pull request #747 from masaohamanaka/master

Targets: RZ_A1H - Fixed I2C bug