riscv: cpufeature: call match_isa_ext() for single-letter extensions

Single-letter extensions may also imply multiple subextensions. For
example, Vector extension implies zve64d, and zve64d implies zve64f.

Extension parsing for "riscv,isa-extensions" has the ability to resolve
the dependency by calling match_isa_ext(). This patch makes deprecated
parser call the same function for single letter extensions.

Signed-off-by: Andy Chiu <andy.chiu@sifive.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20240510-zve-detection-v5-3-0711bdd26c12@sifive.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

Author: AndybnACT

arch/riscv/kernel/cpufeature.c

@@ -468,16 +468,15 @@ static void __init riscv_parse_isa_string(unsigned long *this_hwcap, struct risc
 
 		if (unlikely(ext_err))
 			continue;
+
+		for (int i = 0; i < riscv_isa_ext_count; i++)
+			match_isa_ext(&riscv_isa_ext[i], ext, ext_end, isainfo);
+
 		if (!ext_long) {
 			int nr = tolower(*ext) - 'a';
 
-			if (riscv_isa_extension_check(nr)) {
+			if (riscv_isa_extension_check(nr))
 				*this_hwcap |= isa2hwcap[nr];
-				set_bit(nr, isainfo->isa);
-			}
-		} else {
-			for (int i = 0; i < riscv_isa_ext_count; i++)
-				match_isa_ext(&riscv_isa_ext[i], ext, ext_end, isainfo);
 		}
 	}
 }