SWO logger backend produces no output in 'in place' mode

[mnkp]

Describe the bug
The SWO logger backend produces no output if CONFIG_LOG_IMMEDIATE Kconfig option is enabled. Otherwise it works as expected. The support for SWO backend has been overlooked when the new API for 'in place' mode has recently been added.

To Reproduce
Steps to reproduce the behavior:

1. mkdir build; cd build
2. cmake -DBOARD=efr32_slwstk6061a ../samples/subsys/logging/logger/
   (or any other board with SWO support)
3. configure:
   CONFIG_LOG_BACKEND_SWO=y
CONFIG_LOG_IMMEDIATE=y
4. make flash
5. Start SWO console
6. Reset the board, observe no output

Expected behavior
The log output is printed to SWO console.

Impact
SWO can't be used in 'in place' mode required by SoCs with limited RAM, low power projects.

Environment

• OS: any
• Toolchain: any
• Commit SHA or Version used: v1.14.0-rc3