Fix overapping XMEGA flash memories for dryrun programmer

[stefanrueger]

Fixes #1485:

$ avrdude -qqc dryrun -p x128a1 -T'w boot 0 "bootloader iz ere"' -T"d flash 0x20000 16"
20000  62 6f 6f 74 6c 6f 61 64  65 72 20 69 7a 20 65 72  |bootloader iz er|

$ avrdude -qqc dryrun -p x128a1 -T'w boot 0 "bootloader iz ere"' -Uflash:r:-:I | tail -2
:12000000626F6F746C6F6164657220697A206572650064                             // 20000> bootloader_iz_ere.
:00000001FF

$ avrdude -qqc dryrun -p x128a1 -T'w flash 0x20000 "bootloader iz ere"' -T"d boot 0 16"
0000  62 6f 6f 74 6c 6f 61 64  65 72 20 69 7a 20 65 72  |bootloader iz er|

$ avrdude -qqc dryrun -p x128a1 -T'w flash 0x20000 "bootloader iz ere"' -Uboot:r:-:I
:12000000626F6F746C6F6164657220697A206572650064                             // 00000> bootloader_iz_ere.
:00000001FF

$ avrdude -qqc dryrun -p x128a1 -Uappt:w:'"apptable data"':m -T"read flash 0x1e000 16"
1e000  61 70 70 74 61 62 6c 65  20 64 61 74 61 00 ff ff  |apptable data...|

$ avrdude -qqc dryrun -p x128a1 -Uappt:w:'"apptable data"':m -Uflash:r:-:I | tail -2
:0EE000006170707461626C652064617461000F                                     // 1e000> apptable_data.
:00000001FF

$ avrdude -qqc dryrun -p x128a1 -Uflash:w:'"application pgm"':m -T"read appl 0 16"
00000  61 70 70 6c 69 63 61 74  69 6f 6e 20 70 67 6d 00  |application pgm.|

$ avrdude -qqc dryrun -p x128a1 -Uflash:w:'"application pgm"':m -Uappl:r:-:I
:100000006170706C69636174696F6E2070676D00F8                                 // 00000> application_pgm.
:00000001FF

[MCUdude]

PR workd great, thanks!

[mcuee]

Yes this PR is good to go.

# Wrong: writing to apptable using -U but flash is empty in terminal
PS C:\work\avr\avrdude_test\avrdude_bin> .\avrdude_git -qqc dryrun -p x128a1 -Uappt:w:'"apptable data"':m -T"read flash 0x1e000 16"
1e000  ff ff ff ff ff ff ff ff  ff ff ff ff ff ff ff ff  |................|

#1486 is good
PS C:\work\avr\avrdude_test\avrdude_bin> .\avrdude_pr1486 -qqc dryrun -p x128a1 -Uappt:w:'"apptable data"':m -T"read flash 0x1e000 16"
1e000  61 70 70 74 61 62 6c 65  20 64 61 74 61 00 ff ff  |apptable data...|

PS C:\work\avr\avrdude_test\avrdude_bin> .\avrdude_pr1486 -qqc dryrun -p x128a1 -Uflash:w:'"application pgm"':m -T"read appl 0 16"
00000  61 70 70 6c 69 63 61 74  69 6f 6e 20 70 67 6d 00  |application pgm.|

PS C:\work\avr\avrdude_test\avrdude_bin> .\avrdude_pr1486 -qqc dryrun -p x128a1 -Uflash:w:'"application pgm"':m -Uappl:r:-:I
:100000006170706C69636174696F6E2070676D00F8                                 // 00000> application_pgm.
:00000001FF