drivers/sensors: Add AS5047D magnetic encoder driver

[DheerajSingh1107]

Summary

This PR adds a new SPI-based magnetic encoder driver for the AMS AS5047D.

The AS5047D is a 14-bit on-axis magnetic rotary encoder that communicates over SPI and is commonly used in motor control and robotics applications requiring precise angular position feedback.

This driver provides:

• 14-bit angular position readout (0–16383)
• SPI communication interface compatible with NuttX SPI framework
• Basic error detection using status bits from the device

The implementation follows existing NuttX sensor driver patterns and is designed to be reusable across supported boards.

Impact

• New Feature: Adds support for AS5047D encoder
• No breaking changes: Existing drivers and subsystems are unaffected
• Hardware: Requires an SPI interface (tested on STM32F4 SPI3)
• Build: Adds a new driver option (must be enabled via config)
• Use case: Motor control, robotics, FOC systems requiring precise angle feedback

No impact on existing APIs or backward compatibility.

Testing

Tested on:

• Board: STM32F446re (SPI3)
• Setup: AS5047D connected via SPI with proper CS handling

Test Procedure:

1. Initialized SPI bus and driver in NuttX

2. Performed continuous angle reads

3. Verified:

   • Stable 14-bit output range (0–16383)
   • No constant or stuck values
   • Correct response to shaft rotation

4. Checked error flags in returned data
   Observations:

• Angle values update correctly with rotation
• No communication faults observed under normal operation
• Timing adjustments were required for stable SPI reads
  Logs (example):

[acassis]

@DheerajSingh1107 thank you for your contribution, please align the CMakelist:

if(CONFIG_SENSORS_AS5047D)
  list(APPEND SRCS as5047d.c)
endif()

[linguini1]

Please add documentation for this driver :)

[acassis]

@DheerajSingh1107 please take a look at this PR I submitted to MT6816 (#18807) and add a board config to some board you are using with it and Documentation to your AS5047D, this way a new user will be able to get it working easily