ext: hal: cypress: Protect floating point code with CONFIG_FLOAT

There is a little bit of floating point code in cy_sysclk.c.  For now
add compile protection for this code using CONFIG_FLOAT.  This code
utilizes some libm functions like ceil().  So if / when the functions
Cy_SysClk_EcoConfigure & Cy_SysClk_FllConfigure are needed we'll also
new to probably pull in newlib.

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>