Reading 8- or 16-bit attributes from big-endian device returns 0 (#6166)

[pjzander-signify]

Problem

When reading an 8- or 16-bit attribute from a big endian device the value is 0, despite that defaults other than 0 are defined.

The defaults of these attributes are defined in a zap-file and from that a header file is generated (endpoint_config.h).
This header file contains structures that are used by the software to read cluster information and the attributes of these clusters.
The value of these attributes are stored in a union that also contains 2 pointers:
typedef union { uint8_t * ptrToDefaultValue; uint16_t defaultValue; EmberAfAttributeMinMaxValue * ptrToMinMaxValue; } EmberAfDefaultOrMinMaxAttributeValue;

A generated default value is compiled into that union using an explicit type cast to a pointer.
Example:
{ (uint8_t *) 3 } }
In a 32-bit little-endian the memory layout will be:
03 00 00 00
The 16-bit defaultValue (the first 2 bytes) will have the value 3, which is correct.

In a 32-bit big-endian system the layout will be:
00 00 00 03
The 16-bit defaultValue (the first 2 bytes) will have the value 0, which is not correct.

Summary of Changes

Redefinitions of the unions and update of the zap file.

Fixes #6166

[bzbarsky-apple]

Probably need to rebase on top of master to get ESP32 to pass, because there were some changes to the infrastructure there landing and then being backed out and so on...

[woody-apple]

Probably need to rebase on top of master to get ESP32 to pass, because there were some changes to the infrastructure there landing and then being backed out and so on...

Done

[woody-apple]

@saurabhst @andy31415 ?