bsp/psim: Fix declaration

It declares a symbol defined in the linker command file.
bsps/powerpc: Avoid placement in small-data area
bsp/psim: Use EABI and System V small-data area
bsp/mpc55xx: Round PLL divider up
bsp/mpc55xx: Avoid integer overflow
bsp/mpc55xx: Update due to API changes

Termios notifies now the driver about an inactive transmit with the
length argument set to zero.
posix: Add comment
psxtests/psxhdrs: Fix cleanup push/pop test

The pthread_cleanup_push() and pthread_cleanup_pop() statements must
appear as a pair in the same lexical scope as required by POSIX.
psxtests/psxcleanup: Fix cleanup push/pop test

The pthread_cleanup_push() and pthread_cleanup_pop() statements must
appear as a pair in the same lexical scope as required by POSIX.