CMakeLists: use debuglib_null for Release builds

[Jino26]

When TARGET=Release is set, debug logs such as SpdmReceiveRequest and SpdmSendResponse are still printed because the executables are hardcoded to link with debuglib. The -DLIBSPDM_DEBUG_ENABLE=0 flag only controls compile-time macros but does not switch the linked debug library implementation.

Add a SPDM_DEBUG_LIB_NAME variable in the main CMakeLists.txt that selects debuglib_null for Release builds and debuglib for Debug builds.

[Jino26]

Tested with below flags:

EXTRA_OECMAKE += "\
    -DARCH=${@get_spdm_multiarch(bb, d)} \
        -DTOOLCHAIN=NONE \
        -DTARGET=Release \
        -DCRYPTO=openssl \
        -DENABLE_BINARY_BUILD=1 \
"

Output:

Before:

# spdm_responder_emu --trans TCP
spdm_responder_emu version 0.1
trans - 0x3
context_size - 0x2bf8
Platform server listening on port 4194
Platform port Receive command: 00 00 00 01
Platform port Receive transport_type: 00 00 00 03
Platform port Receive size: 00 00 00 08
Platform port Receive buffer:
    06 00 01 05 10 84 00 00
SpdmReceiveRequest[.] ...
SpdmReceiveRequest[0] msg SPDM_GET_VERSION(0x84), size (0x4):
0000: 10 84 00 00
SpdmSendResponse[0] ...
SpdmSendResponse[0]: msg SPDM_VERSION(0x4), size (0x10):
0000: 10 04 00 00 00 05 00 10 00 11 00 12 00 13 00 14
Platform port Transmit command: 00 00 00 01

After:

# spdm_responder_emu --trans TCP
spdm_responder_emu version 0.1
trans - 0x3
context_size - 0x2bf8
Platform server listening on port 4194
Platform port Receive command: 00 00 00 01
Platform port Receive transport_type: 00 00 00 03
Platform port Receive size: 00 00 00 08
Platform port Receive buffer:
    06 00 01 05 10 84 00 00
Platform port Transmit command: 00 00 00 01
Platform port Transmit transport_type: 00 00 00 03

Only spmd_responder_emu traces are printed now compared to before.

[Jino26]

Fixes #473