Use uint64_t for SVE VQ

Previously VQ was of type long. Using uint64_t ensures it always matches the
same type as the VG register.
Note that in the Linux kernel, VQ is 16bits. We cast it up to 64bits
immediately after reading to ensure we always use the same type throughout
the code.

gdb/
	* aarch64-tdep.c (aarch64_read_description): Use uint64_t for VQ.
	* aarch64-tdep.h (aarch64_read_description): Likewise.
	* arch/aarch64.c (aarch64_create_target_description): Likewise.
	* arch/aarch64.h (aarch64_create_target_description): Likewise.
	* features/aarch64-sve.c (create_feature_aarch64_sve): Likewise.
	* nat/aarch64-sve-linux-ptrace.c(aarch64_sve_get_vq): Likewise.
	* nat/aarch64-sve-linux-ptrace.h (aarch64_sve_get_vq): Likewise.