The pseudo instruction ldr <reg>, =... supports on AArch64 32- and 64-bit
constants. Add support for 64 bit constants for the pools to support the pseudo instruction fully.
Changes the AArch64 ldr-pseudo tests to use 32-bit registers and adds tests with 64-bit registers.
This type is getting a little hard to read. I suggest creating a small struct to represent the constant pool entries and name each field with something meaningful (e.g. Expr, Size, etc).