Incompatible modules in standalone DANKARMULTI

[francesco-scar]

Describe the bug
Some standalone modules are incompatible due to multiple definitions of the same functions, so we get compilation errors.

To Reproduce
Steps to reproduce the behavior:

1. Set STANDALONE=DANKARMULTI in Makefile.platform
2. Edit armsrc/Standalone/dankarmulti.c similarly to the following:

#include "dankarmulti.h"
#define MODE_NAME em4100emul
#define MODE_FILE "lf_em4100emul.c"
#include "dankarmulti.h"
#define MODE_NAME em4100
#define MODE_FILE "lf_em4100rswb.c"
#include "dankarmulti.h"

START_MODE_LIST
ADD_MODE(em4100emul)
ADD_MODE(em4100)
END_MODE_LIST

3. Try to compile with make

Expected behavior
Compile successfully and get the two modules are available in standalone mode

The problem
I didn't searched exhaustively for the same problem with other modules, but with lf_em4100emul and lf_em4100rswb there are the same definitions of

static uint64_t rev_quads(uint64_t bits);
static void fill_buff(uint8_t bit);
static void construct_EM410x_emul(uint64_t id);

so just deleting them in the second file works fine.

Since dankarmulti actually includes the C source files in its own file, the static keyword doesn't help. Possible solutions are moving those common functions into a single, separate file (for example, util) or renaming each function differently in every module (maybe setting the standard to append the module name to each function or something similar). I don't know which one is the clearest solution.