Debug-profile: Use -Og level for GCC_ARM optimization

This brings massive ROM savings, and allows to use debug builds
also with larger applications (for. ex. Mesh stack).

Diff. for mbed-cloud-client-example with Wi-Sun stack.

Total Static RAM memory (data + bss): 85120(-216) bytes
Total Flash memory (text + data): 592668(-329296) bytes

Author: teetak01

tools/profiles/debug.json

@@ -5,7 +5,7 @@
                    "-fmessage-length=0", "-fno-exceptions",
                    "-ffunction-sections", "-fdata-sections", "-funsigned-char",
                    "-MMD", "-fno-delete-null-pointer-checks",
-                   "-fomit-frame-pointer", "-O0", "-g3", "-DMBED_DEBUG",
+                   "-fomit-frame-pointer", "-Og", "-g3", "-DMBED_DEBUG",
                    "-DMBED_TRAP_ERRORS_ENABLED=1"],
         "asm": ["-x", "assembler-with-cpp"],
         "c": ["-std=gnu11"],