Officially name the base extension for hypervisor support: "H"

This is the initial change in the series and does not replace other
references to "the hypervisor extension" to 'the "H" extension'.

Signed-off-by: Tsukasa OI <research_trasio@irq.a4lg.com>

src/hypervisor.adoc

@@ -1,5 +1,5 @@
 [[hypervisor]]
-== Hypervisor Extension, Version 1.0
+== "H" Extension for Hypervisor Support, Version 1.0
 
 This chapter describes the RISC-V hypervisor extension, which
 virtualizes the supervisor-level architecture to support the efficient