[Bug]: Incorrect buffer address used for flashing pyOCD internal targets after double buffering was disabled

[TeoMahnic]

Description

The removal of the default double-buffering mechanism caused some internal targets to fail during programming. The failure occurs because the flash algorithm uses a different buffer address when double buffering is not enabled.

Proposed 3-step solution:

1. Re-enable double buffering mechanism by default only for internal targets. It will then be used based on the existing condition of number of page_buffers available for the given algorithm.
2. Go over all existing internal target algorithms and replace begin_data with a single entry in page_buffers, if page_buffers doesn't already exist. Update flash.py to reflect the changes in algorithms. Remove begin_data from the template in generate_flash_algo.py script.
3. Remove second buffer location entry from page_buffers and correct end_stack for STM32H7xx internal targets, as they are confirmed to have issue with double-buffering mechanism.

Steps to Reproduce

No response

Expected Behavior

No response

Additional Information

No response