This commit resolves issue apache#620:

Remove CONFIG_CAN_PASS_STRUCTS apache#620

The configuration option CONFIG_CAN_PASS_STRUCTS was added many years ago to support an old version of the SDCC compiler. That compiler is currently used only with the Z80 and Z180 targets. The limitation of that old compiler was that it could not pass structures or unions as either inputs or outputs. For example:

    #ifdef CONFIG_CAN_PASS_STRUCTS
    struct mallinfo mallinfo(void);
    #else
    int      mallinfo(FAR struct mallinfo *info);
    #endif

And even leads to violation of a few POSIX interfaces like:

    #ifdef CONFIG_CAN_PASS_STRUCTS
    int  sigqueue(int pid, int signo, union sigval value);
    #else
    int  sigqueue(int pid, int signo, FAR void *sival_ptr);
    #endif

This breaks the 1st INVIOLABLES rule:

Strict POSIX compliance
-----------------------

  o Strict conformance to the portable standard OS interface as defined at
    OpenGroup.org.
  o A deeply embedded system requires some special support.  Special
    support must be minimized.
  o The portable interface must never be compromised only for the sake of
    expediency.
  o Expediency or even improved performance are not justifications for
   violation of the strict POSIX interface

Also, it appears that the current SDCC compilers have resolve this issue and so, perhaps, this is no longer a problem: z88dk/z88dk#1132

NOTE:  This commit cannot pass the PR checks because it depends on matching changes to the apps/ directory.

Run all files modified by PR 766 through nxstyle and fix any resulting complaints.

NOTE:  Numerous "Mixed case identifier" errors in arch/arm/src/cxd56xx/cxd56_gnss.c were not fixed because this problem is of much larger scope than this file.

Modified boards/z80/z180/p112/README.txt and boards/z80/z80/z80sim/README.txt:

IMPORTANT NOTE as of 2020-4-11:  Support for CONFIG_CAN_PASS_STRUCTS was removed in NuttX-9.1.  This was necessary to enforce some POSIX interface compliance but also means that ALL older SDCC versions will no long build with NuttX.  I have been told that the newest SDCC compilers can indeed pass structure and union parameters and return values.  If that is correct, then perhaps the newer SDCC compilers will be used.  Otherwise, it will be necessary to use some other, more compliant compiler.