The zve extension specifies the maximum ELEN for both integer and floating
point mode - defined by macro __riscv_v_elen and __riscv_v_elen_fp.
This commit restricts the functions in riscv_vector.h by the zve defined
Change enum RISCVExtension to RISCVPredefinedMacro since now it
contains not only extensions. Also added type alignment to it.