KVM: selftests: Use SZ_* macros from sizes.h in max_guest_memory_test.c

Replace size_1gb defined in max_guest_memory_test.c with the SZ_1G,
SZ_2G and SZ_4G from linux/sizes.h header file.

Signed-off-by: Vipin Sharma <vipinsh@google.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20221103191719.1559407-5-vipinsh@google.com


Signed-off-by: Sean Christopherson <seanjc@google.com>