lib: Add hexdump

Often during debugging session it's very interesting to see
what data we were dealing with. For example what we write or read
to/from memory or peripherals.

This change introduces functions that allow to dump binary
data with one simple function invocation like:
------------------->8----------------
print_hex_dump_bytes("", DUMP_PREFIX_OFFSET, buf, len);
------------------->8----------------

which gives us the following:
------------------->8----------------
00000000: f2 b7 c9 88 62 61 75 64 72 61 74 65 3d 31 31 35  ....baudrate=115
00000010: 32 30 30 00 62 6f 6f 74 61 72 67 73 3d 63 6f 6e  200.bootargs=con
00000020: 73 6f 6c 65 3d 74 74 79 53 33 2c 31 31 35 32 30  sole=ttyS3,11520
00000030: 30 6e 38 00 62 6f 6f 74 64 65 6c 61 79 3d 33 00  0n8.bootdelay=3.
00000040: 62 6f 6f 74 66 69 6c 65 3d 75 49 6d 61 67 65 00  bootfile=uImage.
00000050: 66 64 74 63 6f 6e 74 72 6f 6c 61 64 64 72 3d 39  fdtcontroladdr=9
00000060: 66 66 62 31 62 61 30 00 6c 6f 61 64 61 64 64 72  ffb1ba0.loadaddr
00000070: 3d 30 78 38 32 30 30 30 30 30 30 00 73 74 64 65  =0x82000000.stde
00000080: 72 72 3d 73 65 72 69 61 6c 30 40 65 30 30 32 32  rr=serial0@e0022
00000090: 30 30 30 00 73 74 64 69 6e 3d 73 65 72 69 61 6c  000.stdin=serial
000000a0: 30 40 65 30 30 32 32 30 30 30 00 73 74 64 6f 75  0@e0022000.stdou
000000b0: 74 3d 73 65 72 69 61 6c 30 40 65 30 30 32 32 30  t=serial0@e00220
000000c0: 30 30 00 00 00 00 00 00 00 00 00 00 00 00 00 00  00..............
...
------------------->8----------------

Source of hexdump.c was copied from Linux kernel v4.7-rc2.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Cc: Anatolij Gustschin <agust@denx.de>
Cc: Mario Six <mario.six@gdsys.cc>
Cc: Simon Glass <sjg@chromium.org>
Cc: Tom Rini <trini@konsulko.com>
Cc: Stefan Roese <sr@denx.de>