dump: Update correct kdump phys_base field for AArch64

dump: Update correct kdump phys_base field for AArch64

For guest kernel that supports KASLR, the load address can change every
time when guest VM runs. To find the physical base address correctly,
current QEMU dump searches VMCOREINFO for the string "NUMBER(phys_base)=".
However this string pattern is only available on x86_64. AArch64 uses a
different field, called "NUMBER(PHYS_OFFSET)=". This patch makes sure
QEMU dump uses the correct string on AArch64.

Signed-off-by: Wei Huang <[email protected]>
Reviewed-by: Marc-André Lureau <[email protected]>
Message-id: 1520615003[email protected]
Signed-off-by: Peter Maydell <[email protected]>