refactor: move kernel_va_map.h to include/arch/x86/, clean virtio_blk.c port I/O

refactor: move kernel_va_map.h to include/arch/x86/, clean virtio_blk.c port I/O

- kernel_va_map.h: moved from include/ to include/arch/x86/ since it
  contains x86-specific VA layout (IOAPIC, LAPIC, ATA DMA, E1000)
- Updated all 8 include sites to use new path
- virtio_blk.c: removed duplicated port I/O inline asm, now uses
  io.h → arch/x86/io.h (outb/inb/outw/inw/outl/inl)
- Renamed outb_port/inb_port to standard outb/inb

Deep search results — agnostic areas verified clean:
- src/kernel/: no arch-specific code
- src/mm/: no arch-specific code
- src/drivers/: no arch-specific code (after virtio_blk fix)
- src/net/: no arch-specific code
- include/ (excl arch/): only dispatcher-pattern #includes remain
  (io.h, interrupts.h, arch_types.h, arch_syscall.h, spinlock.h)