Add memory sram at the expense of data

The memory data was introduced for the sole purpose to provide an
nvm_data_offset for Microchip programmers. As an address offset it would
tell programmers to read/write in data space. It so turned out that this
nvm_data_offset always was 0x1000000 for PDI and UPDI parts.

This commit removes this artificial data memory and treats the data offset
in the code as what it currently is: a constant.

At the same time the commit introduces an sram memory with offset and size
for virtually all parts known to AVRDUDE.

src/avr.c

@@ -1528,7 +1528,7 @@ memtable_t avr_mem_order[100] = {
   {"bootrow",     MEM_BOOTROW | MEM_USER_TYPE},
   {"usersig",     MEM_USERROW | MEM_USER_TYPE},
   {"userrow",     MEM_USERROW | MEM_USER_TYPE},
-  {"data",        MEM_SRAM},
+  {"sram",        MEM_SRAM},
   {"io",          MEM_IO},
   {"sib",         MEM_SIB | MEM_READONLY},
 };