Libc math: Error fixes in modf() and ceil() API's

Approved-by: Gregory Nutt <gnutt@nuttx.org>

Ex:for input x = 1.0, the ouput should be 1.0, but the ouput was 2.0.

Signed-off-by: Lokesh B V <lokeshbv333@gmail.com>

The sign of integral part given by the modf() should be same as sign of input.
But for inputs between 0 and 1, the sign of integral part was not same as sign of input.

Signed-off-by: Lokesh B V <lokeshbv333@gmail.com>

Initial port to STM32F769I-DISCO

Approved-by: Gregory Nutt <gnutt@nuttx.org>

do not enforce CONFIG_STM32_CCMEXCLUDE for CONFIG_ARCH_CHIP_STM32F7, macro rename STM32 -> STM32F7, #include corrections