riscv: convert the t-head pbmt errata to use the __nops macro

Instead of manually inserting the list of nops, use the recently
introduced __nops(n) macro to make everything more readable.
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/include/asm/errata_list.h

@@ -68,13 +68,7 @@ asm(ALTERNATIVE_2("li %0, 0\t\nnop",					\
  */
 #define ALT_THEAD_PMA(_val)						\
 asm volatile(ALTERNATIVE(						\
-	"nop\n\t"							\
-	"nop\n\t"							\
-	"nop\n\t"							\
-	"nop\n\t"							\
-	"nop\n\t"							\
-	"nop\n\t"							\
-	"nop",								\
+	__nops(7),							\
 	"li      t3, %2\n\t"						\
 	"slli    t3, t3, %4\n\t"					\
 	"and     t3, %0, t3\n\t"					\