style: Fix __riscv consistency with other ISAs

The defines for the majority of other instruction set architectures are
of the form `__isa-name__` while RISC-V was `__isa-name`.  This makes
the relevant changes to keep the definition structure consistent.

include/asm.h

@@ -19,7 +19,7 @@ static inline uint64_t read_counter(void)
         __asm__ __volatile__ ("mrs %0, pmccntr_el0" : "=r" (val));
 #elif defined(__arm__)
         __asm__ __volatile__ ("mrc p15, 0, %0, c9, c13, 0" : "=r" (val));
-#elif defined(__riscv) && __riscv_xlen == 64
+#elif defined(__riscv__) && __riscv_xlen == 64
 	__asm__ __volatile__ ("csrr %0, 0xc01" : "=r" (val) : : "memory");
 #else
 #error unsupported arch

include/system/stdarg.h

@@ -24,7 +24,7 @@ typedef __builtin_va_list __builtin_sysv_va_list;
 #endif
 
 #if defined(__aarch64__) || defined(__arm__) || defined(__i386__) || \
-	defined(__i486__) || defined(__i686__) || defined(__COVERITY__) || defined(__riscv)
+	defined(__i486__) || defined(__i686__) || defined(__COVERITY__) || defined(__riscv__)
 
 typedef __builtin_va_list ms_va_list;
 typedef __builtin_va_list __builtin_ms_va_list;

pe-relocate.c

@@ -280,7 +280,7 @@ allow_64_bit(void)
 	if (in_protocol)
 		return 1;
 	return 0;
-#elif defined (__riscv) && __riscv_xlen == 64
+#elif defined (__riscv__) && __riscv_xlen == 64
 	return 1;
 #else /* assuming everything else is 32-bit... */
 	return 0;
@@ -302,7 +302,7 @@ allow_32_bit(void)
 	return 1;
 #elif defined(__aarch64__)
 	return 0;
-#elif defined (__riscv) && __riscv_xlen == 64
+#elif defined (__riscv__) && __riscv_xlen == 64
 	return 0;
 #else /* assuming everything else is 32-bit... */
 	return 1;
@@ -330,7 +330,7 @@ static const UINT16 machine_type =
 	IMAGE_FILE_MACHINE_I386;
 #elif defined(__ia64__)
 	IMAGE_FILE_MACHINE_IA64;
-#elif defined(__riscv) && __riscv_xlen == 64
+#elif defined(__riscv__) && __riscv_xlen == 64
 	IMAGE_FILE_MACHINE_RISCV64;
 #else
 #error this architecture is not supported by shim

shim.h

@@ -128,7 +128,7 @@
 #endif
 #endif
 
-#if defined(__riscv) && __riscv_xlen == 64
+#if defined(__riscv__) && __riscv_xlen == 64
 #ifndef DEFAULT_LOADER
 #define DEFAULT_LOADER L"\\grubriscv64.efi"
 #endif