include: Make sbi_current_hartid() as macro in riscv_asm.h

The sbi_current_hartid() being a regular function is quite
expensive because for callers it is a function call instead
of a direct CSR read. This patch converts sbi_current_hartid()
into a macro in riscv_asm.h.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Atish Patra <atish.patra@wdc.com>

include/sbi/riscv_asm.h

@@ -157,6 +157,8 @@ void csr_write_num(int csr_num, unsigned long val);
 		__asm__ __volatile__("wfi" ::: "memory"); \
 	} while (0)
 
+/* Get current HART id */
+#define current_hartid()	((unsigned int)csr_read(CSR_MHARTID))
 
 /* determine CPU extension, return non-zero support */
 int misa_extension_imp(char ext);