Fix some drivers bugs.

Changes as below.

-I2C
 Change communication wait time and Frequency accuracy improvement of I2C.
  - Frequency accuracy improvement
  - Changed the wait time between one communication completed and the next communication start.
    The wait time will be Low clock width by this changing.

-PWM
 Modify processing of pulsewidth() of PWM
  - Modify processing of pulsewidth() to match the specifications of the RZ_A1H.

-SPI
 Fixed a bug that SPI driver is not able to communicate when transfer bit length is 16bit or 32bit.
  - Frequency accuracy improvement
  - Modify transfer processing when transfer bit length is 16bit or 32bit.

-Serial
 Change the reference register macro of Serial
  - Change the reference register macro to align with other driver codes.
Modify some settings of OS and Ether

 - Change default setting of CMSIS-RTOS RTX for Cortex-A9 to align with Cortex-M.
 - Change the interrupt priority of Ether driver to align with other drivers.
Merge pull request #802 from masaohamanaka/master

Targets: RZ_A1H - Fix some drivers bugs and modify some settings of OS and