Fix rgblink banks

Fixed WRAMX, VRAM and SRAM banks.

1. WRAMX banks were off by 1. Setting WRAMX,BANK[1] made the linker output to bank 2. That has been fixed, banks 1 to 7 output to the correct one.
2. When using BANK() with a symbol in WRAMX, VRAM or SRAM, the linker would return a value based on "link/assign.h" banks instead of the Game Boy bank. Now, it returns the correct number.
3. When generating the mapfile, global symbols of those sections (and sections) didn't appear, only SLACK.
4. Also, improved the output a bit: Updated the "created by" string in symfiles (it named the linker xLink instead of RGBLink)