shell_fprintf requires that formatted output be emitted with a
putchar()-like output function. Newlib does not provide such a
capability. Zephyr provides two solutions: z_prf() which is part of
minimal libc and handles floating point formatting, and z_vprintk()
which is core and does not support floating point.
Move z_prf() out of minimal libc into the core lib area, and use it
unconditionally in the shell.
Signed-off-by: Peter Bigot <peter.bigot@nordicsemi.no>
e812ee6c21