refactor(spi_flash): move internal types to private headers and refactor initialization

This commit refactors the SPI flash component to improve encapsulation and
modularity by moving internal types and functions to private headers, and
reorganizing initialization code.

Key changes:

1. Move PSRAM frequency constraint macro from soc_caps.h to mspi_ll.h
   - Rename SOC_SPI_MEM_PSRAM_FREQ_AXI_CONSTRAINED to
     MSPI_TIMING_LL_PSRAM_FREQ_AXI_CONSTRAINED
   - Move macro definition to chip-specific mspi_ll.h files (C5, C61, H4, P4, S31)
   - Update usage in clk_utils.c and esp_flash_spi_init.c
   - Remove old macro from all soc_caps.h files

2. Move internal types to private headers
   - Move esp_flash_t structure to esp_private/esp_flash_types.h
   - Move esp_flash_os_functions_t to esp_private/spi_flash_os.h
   - Update all internal files to include private headers
   - Keep forward declarations in public esp_flash.h

3. Move chip driver header to internal directory
   - Move spi_flash_chip_driver.h to esp_flash_port/spi_flash_chip_driver.h
   - Update all references to use new path
   - Add esp_private/esp_flash_types.h include to the moved header

4. Refactor initialization functions
   - Move init_flash from esp_system/startup_funcs.c to
     spi_flash/esp_flash_spi_init.c
   - Create new init_pm_flash_freq_limit function in startup_funcs.c
     to call esp_pm_flash_freq_limit_init() conditionally
   - Update system_init_fn.txt with new function locations

5. Improve API encapsulation
   - Replace direct access to esp_flash_t->size in
     esp_partition_register_external() with esp_flash_get_size() API
   - Move esp_flash_is_quad_mode from inline function to regular function
     in esp_flash_api.c

6. Update component dependencies
   - Add esp_driver_gpio to spi_flash component PRIV_REQUIRES
   - Remove unused includes and clean up header dependencies

These changes improve code organization by clearly separating public APIs
from internal implementation details, making the codebase more maintainable
and reducing the risk of breaking changes to internal structures.

components/esp_hal_mspi/esp32s31/include/hal/mspi_ll.h

@@ -44,6 +44,9 @@ extern "C" {
 #define MSPI_TIMING_LL_MSPI_ID_0                      0
 #define MSPI_TIMING_LL_MSPI_ID_1                      1
 
+// PSRAM frequency should be constrained by AXI frequency to avoid FIFO underflow.
+#define MSPI_TIMING_LL_PSRAM_FREQ_AXI_CONSTRAINED    1
+
 #define MSPI_LL_AXI_DISABLE_SUPPORTED                 1
 #define MSPI_LL_INTR_EVENT_SUPPORTED                  1