x86: Split large structs into portions

The C parser does not enjoy parsing structs with many fields

x86: Correct multiboot info definition

The fields in the multiboot_info structure have precise sizes and should not use pointers
types as these sizes change between ia32 and x86_64 builds. This commit changes such
fields to be the correct fixed size uint32_t

x86: Pass VBE information from multiboot through bootinfo

x86: Populate the freemem list from the multiboot mem list

If the multiboot memory list exists, then it may contain more
than just the single contiguous memory region listed in 'mem_upper'
Therefore we use it to populate a more complete free memory list,
if it exists

x86: Make x86 the name of the architecture instead of IA32

IA32 is 32bit version of the x86 architecture. Whilst only IA32
is supported, much of the code is generic x86. Using a generic
x86 architecture will aid in future 64bit support