soc: intel_adsp/ace: put syscall helpers in vector code section

This puts the syscall helpers into the vector code section, and
is a tiny TLB optimization. Before this, worst case scenario is
that there would 2 instruction TLB misses when both the syscall
helpers and the vector code pages are not in TLB cache. With
this change, there would be at most 1 instruction TLB miss as
now the syscall helper and the vector code (which includes
exception handling code and xtensa_do_syscall()) are now in
the same page, and the same TLB entry.

Signed-off-by: Daniel Leung <daniel.leung@intel.com>