perf annotate: add Alpha instruction support

Teach perf annotate about the Alpha control-transfer instructions so jump/call/
return arrows and cross-CPU annotation work for Alpha perf.data.

Add tools/perf/util/annotate-arch/annotate-alpha.c with arch__new_alpha() and an
associate_instruction_ops() that classifies:
  call:   bsr, jsr, jsr_coroutine
  ret:    ret
  jump:   br, jmp, and the conditional branches beq/bne/blt/ble/bgt/bge/blbc/
          blbs and fbeq/fbne/fblt/fble/fbgt/fbge
  mov:    mov, fmov (objdump pseudos)

EM_ALPHA is 0x9026, far too large to index the e_machine-keyed arch_new_fn[]
table in arch__find(), so select arch__new_alpha explicitly before the table
lookup. Declare it in disasm.h and add the object to the annotate-arch Build.

Disassembly itself comes from objdump/binutils, which already supports Alpha;
this provides perf's instruction-class metadata for annotation.