Fix PBES and OMAC flag scopes

[UnknownDK]

pbes_properties and omac_state are gatekept by LTC_PBES and LTC_OMAC respectively. Therefore they should only be used within those scopes.

[UnknownDK]

Fixes these errors with LTC_NOTHING.

 ~/r/libtomcrypt> make CFLAGS="-DLTC_NOTHING"                                                                                            2 develop
   * cc src/ciphers/aes/aes.o
In file included from src/ciphers/aes/aes.c:25:
./src/headers/tomcrypt_private.h:114:10: error: unknown type name ‘pbes_properties’
  114 |    const pbes_properties *data;
      |          ^~~~~~~~~~~~~~~
./src/headers/tomcrypt_private.h:182:19: error: unknown type name ‘omac_state’
  182 | int omac_vprocess(omac_state *omac, const unsigned char *in,  unsigned long inlen, va_list args);
      |                   ^~~~~~~~~~
make: *** [makefile:64: src/ciphers/aes/aes.o] Error 1