RGBLINK `-t/--tiny` and `-w/--wramx` do not allow the linkerscript to omit bank number

The rgblink(5) man page for linkerscripts claims:

> The bank number can be omitted from the types that only contain a single bank, which are: ROM0, ROMX if `-t` is passed to rgblink, VRAM if `-d` is passed to rgblink, WRAM0, WRAMX if `-w` is passed to rgblink, OAM, and HRAM.

However, it's not actually allowed:

```console
$ cat foo.asm
SECTION "test", ROMX
Label:: db 42
$ cat foo.link
ROMX
"test"
$ ./rgbasm -o foo.o foo.asm
$ ./rgblink -t -l foo.link foo.o
error: A bank number must be specified for ROMX
at foo.link(1)
Linking failed with 1 error
```