x86: Do not implicitly mask virtual address when mapping frames
x86: Do not implicitly mask virtual address when mapping frames

This mask made the checkVPAlignment call completely redundant. By
removing this mask and relying on the check we bring the x86 in line
with the ARM behaviour

cmr/seL4,cmr/seL4,cmr/seL4,zhicheng/seL4,zhicheng/seL4,zhicheng/seL4