Rename macro functions starting with two or three underscores

[pfl]

In kernel/ directory the following code snippet of function looking macros starting with two and three underscores are defined:

#define Z_SYSCALL_CONCAT(arg1, arg2) __SYSCALL_CONCAT(arg1, arg2)
#define __SYSCALL_CONCAT(arg1, arg2) ___SYSCALL_CONCAT(arg1, arg2)
#define ___SYSCALL_CONCAT(arg1, arg2) arg1##arg2

#define Z_SYSCALL_NARG(...) __SYSCALL_NARG(__VA_ARGS__, __SYSCALL_RSEQ_N())
#define __SYSCALL_NARG(...) __SYSCALL_ARG_N(__VA_ARGS__)
#define __SYSCALL_ARG_N(_1, _2, _3, _4, _5, _6, _7, N, ...) N
#define __SYSCALL_RSEQ_N() 6, 5, 4, 3, 2, 1, 0

The macro with only one leading underscore was renamed earlier in #13379 to start with the 'Z_' prefix. The issue to be fixed is to find a suitable prefix for the rest of the macros starting with __ and ___.

[pfl]

This issue belongs to #9882