Add epmp to extensions list and rename it to smepmp

Add epmp to extensions list and rename it to smepmp

Smepmp is a ratified extension which qemu refers to as epmp.
Rename epmp to smepmp and add it to extension list so that
it is added to the isa string.

Signed-off-by: Himanshu Chauhan <hchauhan@ventanamicro.com>
Signed-off-by: Mayuresh Chitale <mchitale@ventanamicro.com>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20231019065546.1431579-1-mchitale@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>