Update the changelog and revision version in preparation of v1.0-rc1

As per the new versioning policy defined by RVI, the first ratified
version should start with 1.0.

Update the version number and the changelog to reflect that.

Signed-off-by: Atish Patra <atishp@rivosinc.com>

riscv-sbi.adoc

@@ -3,7 +3,7 @@
 = RISC-V Supervisor Binary Interface Specification
 :author: RISC-V Platform Specification Task Group
 :email: tech-unixplatformspec@lists.riscv.org
-:revnumber: 0.3.0
+:revnumber: 1.0-rc1
 :sectnums:
 :xrefstyle: short
 :toc: macro
@@ -27,6 +27,9 @@ https://creativecommons.org/licenses/by/4.0/.
 [preface]
 == Change Log
 
+=== Version 1.0-rc1
+* A typo fix
+
 === Version 0.3.0
 * Few typo fixes
 * Updated the LICENSE with detailed text instead of a hyperlink