binarybuffer: str_to_buf(): align prefix to TCL syntax

binarybuffer: str_to_buf(): align prefix to TCL syntax

Integer values are interpreted by TCL as decimal, binary, octal
or hexadecimal if prepended with '0d', '0b', '0o' or '0x'
respectively.
The case of '0' prefix has been interpreted as octal till TCL 8.6
but is interpreted as part of a decimal number by JimTCL and from
TCL 9.

Align str_to_buf() to latest TCL syntax by:
- addding support for '0d', '0b' and '0o' prefix;
- dropping support for '0' prefix.

Change-Id: I708ef72146d75b7bf429df329a0269cf48700a44
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/8465
Tested-by: jenkins
Reviewed-by: Jan Matyas <jan.matyas@codasip.com>