boards/xtensa/esp32: increase MM_REGIONS for psram defconfig

[fdcavalcanti]

Summary

• boards/xtensa/esp32: increase MM_REGIONS for psram defconfig

Increase MM_REGIONS from 5 to 6 to accomodate latest changes from
initialization refactor.

This change was necessary since the arch init changes on #18832. We fixed some issues on ESP32-S3 but seems we forgot about this one.

Impact

Impact on user: Fix esp32-devkitc:psram boot when DEBUG_ASSERTIONS are enabled.

Impact on build: No.

Impact on hardware: No.

Impact on documentation: No.

Impact on security: No.

Impact on compatibility: No.

Testing

Build the psram defconfig before and after the change.

Building

• ./tools/configure.sh esp32-devkitc:psram
• Enable DEBUG_ASSERTIONS
• Build and flash

Results

Before changes:

[CPU0] mm_addregion: mm_addregion: idx=5, heapstart=0x3ffe4360, heapsize=3792
[CPU0] dump_assert_info: Current Version: NuttX  12.13.0 e226a634fb-dirty May 20 2026 14:52:26 xtensa
[CPU0] dump_assert_info: Assertion failed idx < 5: at file: mm_heap/mm_initialize.c:118 task(CPU0): AppBringUp process: Kernel 0x400d1f38
[CPU0] up_dump_register:    PC: 40086621    PS: 00060223

After changes:
System boots fine.

NuttShell (NSH) NuttX-12.13.0
nsh> free
      total       used       free    maxused    maxfree  nused  nfree name
      98304       8648      89656      11120      87600      5      2 esp32-imem
    4401224       4296    4396928       4712    4194288     44      7 Umem