fix: move VBE framebuffer VA from 0xD0000000 to 0xE0000000

fix: move VBE framebuffer VA from 0xD0000000 to 0xE0000000

The kernel heap starts at KHEAP_START=0xD0000000 and spans 10MB.
The VBE framebuffer was also mapped at 0xD0000000, causing a
virtual address collision that would corrupt the heap when a
framebuffer is present.

Move VBE mapping to 0xE0000000 which is safely above the heap.

Passes: make, cppcheck, QEMU smoke test.