[BIOS] system: IRAM memory management

[asiekierka]

This covers the following API calls:

• INT 17h/AH=0Fh: sys_alloc_iram
• INT 17h/AH=10h: sys_free_iram
• INT 17h/AH=11h: sys_get_my_iram

[asiekierka]

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[asiekierka]

The initial implementation works well enough, but some games (Self Produce) stress it to a level where its possibilities appear insufficient.