Add refcount tracking for ACPICA's mappings and use VIRT_KERNEL_MAP area

[wipawel]

ACPICA maps and unmaps memory in chunks whose address (or size) might not
be PAGE_SIZE aligned. It might for example map memory at address 0x00 and
map another chunk at address 0x40. KTF performs memory (un)mapping using
PAGE_SIZE aligned memory frames. If ACPICA allocates memory at 0x00 and 0x40,
KTF maps the same physical frame to the same virtual address twice.
This does not hurt, but ACPICA can unmap the memory chunk at address 0x40
and assume the chunk at 0x00 is still mapped. KTF will simply unmap entire
frame.

As of now KTF does not need to track mapped frames refcounting based on
smaller granularity than PAGE_SIZE. If a 4K frame is mapped (even multiple
times) and then unmapped once, the frame should be unmapped as a result.

To make ACPICA work with this, add mapped_frames list tracking ACPICA
mapped frames with refcounting. If a frame is mapped several times, it gets
really unmapped only if the same number of times it has been unmapped by
ACPICA.