att: format far pointers as $seg,$off instead of seg:off

the AT&T formatter has no pointer-operand handler of its own, so far branches like lcall/ljmp ptr16:16|32 fell through to the shared printer and came out as seg:offset, which is Intel syntax that gas and objdump reject, so the output would not reassemble. this adds an AT&T-specific pointer printer that emits $segment,$offset with the $ immediate marker and a comma, mirroring gas/objdump and the comma style already used inside AT&T memory operands. a decoded 9a ad ea dd e4 4e 6d now formats as lcall $0x6D4E,$0xE4DDEAAD and reassembles to the same bytes; the jmp_far_16/32 cases are rebased and both regression suites pass.