RISCV/asm: Use CALL rather than JAL

JAL has a maximium displacement of 2M.  To branch further, it needs pairing
with an AUIPC instruction.  CALL is a pseudoinstruction which allows the
linker to pick the appropriate sequence when relaxations are enabled.

This avoids a build failure of the form:

  prelink.o: in function `start':
  xen/xen/arch/riscv/riscv64/head.S:28:(.text.header+0x2c):
  relocation truncated to fit: R_RISCV_JAL against symbol `calc_phys_offset' defined in .init.text section in prelink.o
  make[3]: *** [arch/riscv/Makefile:18: xen-syms] Error 1

when Xen gets large enough, e.g. with CONFIG_UBSAN enabled.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
Release-Acked-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>

xen/arch/riscv/entry.S

@@ -49,7 +49,7 @@ save_to_stack:
         REG_S   t0, CPU_USER_REGS_SSTATUS(sp)
 
         mv      a0, sp
-        jal     do_trap
+        call    do_trap
 
 restore_registers:
         /* Restore stack_cpu_regs */

xen/arch/riscv/riscv64/head.S

@@ -28,7 +28,7 @@ FUNC(start)
         add     t3, t3, __SIZEOF_POINTER__
         bltu    t3, t4, .L_clear_bss
 
-        jal     reset_stack
+        call    reset_stack
 
         /*
          * save hart_id ( bootcpu_id ) and dtb_base as a0 and a1 register can
@@ -37,16 +37,16 @@ FUNC(start)
         mv      s0, a0
         mv      s1, a1
 
-        jal     calc_phys_offset
+        call    calc_phys_offset
         mv      s2, a0
 
-        jal     setup_initial_pagetables
+        call    setup_initial_pagetables
 
         /* Calculate proper VA after jump from 1:1 mapping */
         la      a0, .L_primary_switched
         sub     a0, a0, s2
 
-        jal     turn_on_mmu
+        call    turn_on_mmu
 
 .L_primary_switched:
         /*
@@ -54,11 +54,11 @@ FUNC(start)
          * recalculated after jump from 1:1 mapping world as 1:1 mapping
          * will be removed soon in start_xen().
          */
-        jal     reset_stack
+        call    reset_stack
 
         /* Xen's boot cpu id is equal to 0 so setup TP register for it */
         li      a0, 0
-        jal     setup_tp
+        call    setup_tp
 
         /* restore hart_id ( bootcpu_id ) and dtb address */
         mv      a0, s0