libsel4vm: Fault: support 64 bits fault data mask for aarch64

[colorglass]

The function fault_get_data_mask() only produce the mask within 32 bits which meas it can't return a mask like 0xffffffff00000000 with 64 bits seL4_Word.

seL4_projects_libs/libsel4vm/src/arch/arm/fault.c

Line 494 in eb42051

mask <<= (addr & 0x3) * 8;

Thus for some data structures like GICD_IROUTER of gicv3 which is in 64 bits width, the mask and the related fault function fault_emulate() can't handler the access to the upper 32 bits correctly.