kconfig: logging: Add LOG_MIPI_SYST_ARGS_BUFFER_SIZE option.

Add user configurable LOG_MIPI_SYST_ARGS_BUFFER_SIZE Kconfig
option to use it for macro MIPI_SYST_PCFG_PRINTF_ARGBUF_SIZE.
Moving macro definition of MIPI_SYST_PCFG_PRINTF_ARGBUF_SIZE
from mipi-sys-t library to platform.h which defaulted to 1kb
and resulted in stack overflow in some applications.
LOG_MIPI_SYST_ARGS_BUFFER_SIZE gives flexibilty to users when
maximum log length is known.

Fixes zephyrproject-rtos/mipi-sys-t#10

Signed-off-by: Aastha Grover <aastha.grover@intel.com>