tests: gdb_loadable_elf: adjust the breakpoint location for ESP32 ECO3

The previous location was the return from the first ets_printf call
that prints ROM sign-on message. Since the main function was patched
in ECO3, the new address no longer works — there is no instruction at
0x40007901 in ECO3 ROM. This could be solved by setting two
breakpoints (one would work for ECO <=2, the other for ECO3), but we
would need to remove the unused breakpoint later.
Fix this by setting the breakpoint at ets_printf. This means that when
debugging a loadable ELF the ROM sign-on message will no longer be
shown, but this doesn't seem to be an issue.

Kconfig

@@ -154,7 +154,7 @@ mainmenu "Espressif IoT Development Framework Configuration"
                     mon reset halt
                     # Run to a specific point in ROM code,
                     #  where most of initialization is complete.
-                    thb *0x40007901
+                    thb *0x40007d54
                     c
                     # Load the application into RAM
                     load

tools/test_apps/system/gdb_loadable_elf/gdbinit_esp32

@@ -5,7 +5,7 @@ target remote 127.0.0.1:3333
 mon reset halt
 # Run to a specific point in ROM code,
 #  where most of initialization is complete.
-thb *0x40007901
+thb *0x40007d54
 c
 # Load the application into RAM
 load