Add driver for the ST L3GD20 3 axis gyro

Approved-by: Gregory Nutt

Allow board to configure HSE clock in bypass-mode. This is needed to enable HSE with Nucleo-F746ZG board.

LM3S Ethernet: Fix interrupt work in the last big commit.

Approved-by: Gregory Nutt

C library:  Add ffs().  Add strings.h.  Move strcasecmp, strncasecmp, bzero, bcmp, and bcopy to where they belong in strings.h.h, not string.h.  bzero, bcmp, and bcopy are legacy functions; the contemporary counterparts should be used instead.

Don't build libc/pthread if pthreasa are disable.  Fix a warning in dirent logic if mountpoints are disabled.

Fix for SAMv7 SPI: DLYBS value wass calculated, but never written to any registers. This led to incorrect timings on the bus.

Kinetis Ethernet fix, add FTM3

Approved-by: Gregory Nutt