DaVinci DA8xx: fix set_cpu_clk_info()

DaVinci DA8xx: fix set_cpu_clk_info()

For the DA8xx family of SoCs, the set_cpu_clk_info() function was not
initialising the DSP frequency, leading to 'bdinfo' command output such as:

  [...snip...]
  ARM frequency = 300 MHz
  DSP frequency = -536870913 MHz
  DDR frequency = 300 MHz

This commit provides a separate implementation of set_cpu_clk_info() for
the DA8xx SoCs that initialises the DSP frequency to zero (since
currently the DSP is not enabled by U-Boot on any DA8xx platform). The
separate implementation is justified because there is no common code
between DA8xx and the other SoC families. It is now much easier to
understand the flow of the two separate functions.

Signed-off-by: Laurence Withers <lwithers@guralp.com>
Cc: Tom Rini <trini@ti.com>
Cc: Hadli, Manjunath <manjunath.hadli@ti.com>
Cc: Heiko Schocher <hs@denx.de>