Add RISC-V 64-bit (riscv64) platform support

[gounthar]

The hooks API does not recognize linuxriscv64 as a platform identifier.

Changes needed

1. domain.scala: add case for "linuxriscv64" and define val LinuxRISCV64 = Platform("LINUX_RISCV64", "Linux RISC-V 64bit", Some("riscv64gc-unknown-linux-gnu"))

Related

• feat: add RISC-V 64-bit platform support sdkman-cli#1496, feat: add RISC-V 64-bit platform support sdkman-cli-native#375, feat: add RISC-V 64-bit platform support sdkman-disco-integration#46, feat: add RISC-V 64-bit (riscv64) platform support vendor-release#17, feat: add RISC-V 64-bit (riscv64) platform support sdkman-broker-2#10