HV:refine 'apic_page' & 'pir_desc' in 'struct acrn_vlapic'

 - update 'apic_page' field in 'struct acrn_vlapic',
   from pointer type to 'struct lapic_regs' type.

 - delete 'pir' and update 'pir_desc' to 'vlapic_pir_desc'
   type.

 - fix potential memory leak in 'vlapic_create()'
   should free allocated memory in case of registering
   mmio handler failure.

Signed-off-by: Yonghua Huang <yonghua.huang@intel.com>

Author: yonghuah