Fix ARMV9SME/VORTEXM4 GEMM compilation with SMP disabled

[al3xtjames]

gemm.c currently declares gotoblas_corename in SMP-enabled builds, but the ARMV9SME and VORTEXM4 targets call gotoblas_corename even when SMP is disabled. Fix compilation of the ARMV9SME and VORTEXM4 targets with SMP disabled by unconditionally declaring gotoblas_corename for DYNAMIC_ARCH builds.

The compilation error can be reproduced with make DYNAMIC_ARCH=1 USE_THREAD=0:

gemm.c:558:12: error: call to undeclared function 'gotoblas_corename'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
  558 | if (strcmp(gotoblas_corename(), "armv9sme") == 0
      |            ^