MemMap: Renamed "GSP" heap to "linear", as this is not specific to GSP.

- Linear simply indicates that the mapped physical address is always MappedVAddr+0x0C000000, thus this memory can be used for hardware devices' DMA (such as the GPU).
APT_U: Added GetSharedFont service function.

- TODO: Actually put shared_font in ram
APT_U: Enable shared font loading into RAM.