misc/arm: Correctly name bit in the booting document

SCTLR_EL3.HCR does not exists in the documentation (see D7.2.80 in ARM
DDI 0487A.j). It was meant to be SCTRL_EL3.HCE.

Signed-off-by: Julien Grall <julien.grall@arm.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>

docs/misc/arm/booting.txt

@@ -31,7 +31,7 @@ Xen relies on some settings the firmware has to configure in EL3 before starting
 
 * Xen must be entered in NS EL2 mode
 
-* The bit SCR_EL3.HCR (resp. SCR.HCE for 32-bit ARM) must be set to 1.
+* The bit SCR_EL3.HCE (resp. SCR.HCE for 32-bit ARM) must be set to 1.
 
 
 [1] linux/Documentation/arm/Booting