tiny-printf: Handle %pM format when CONFIG_SPL_NET_SUPPORT is enabled

tiny-printf: Handle %pM format when CONFIG_SPL_NET_SUPPORT is enabled

%pM format string is used to print MAC-address and this is required while SPL
network boot.

This patch fixes the SPL boot issues like the following:

    Trying to boot from USB eth
    ## Error: flags type check failure for "ethaddr" <= "40309614M" (type: m)
    ## Error inserting "ethaddr" variable, errno=1
    eth0: eth_cpsw## Error: flags type check failure for "eth1addr" <=
    "81f01114M" (type: m)
    ## Error inserting "eth1addr" variable, errno=1
    , eth1: usb_ether
    eth_cpsw Waiting for PHY auto negotiation to complete......... TIMEOUT !
    Problem booting with BOOTP
    SPL: failed to boot from all boot devices
    ### ERROR ### Please RESET the board ###

Signed-off-by: Matwey V. Kornilov <matwey.kornilov@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>