Could anybody tell me how to boot up a processor in AARCH32 bit mode in Arm V8 and A53 core?

When the A53 comes out of reset, the initial Execution state (AArch32 or AArch64) is controlled by a signal AA64nAA32

http://infocenter.arm.com/help/topic/com.arm.doc.ddi0500g/BABJAGDF.html

This sets the Execution state of EL3, and this cannot be changed without another reset.

The Execution state of lower ELs (EL2/EL1/EL0) is set by software and can be changed dynamically.  For example, to drop from EL3 (using AArch64) to EL2 (using AArch32):

  MSR      SCTLR_EL2, xzr

  MOV      w1, wzr
  ORR      w1, w1, #1          ; Set NS bit
  ORR      w1, w1, #(1 << 8)   ; Set HCE bit (enabled HVC)
  MSR      SCR_EL3, x1

  ADR      x1, el2_entry_aarch32
  MSR      ELR_EL3, x1

  LDR      x1, =0x1A            ; Bit pattern AArch32 Hyp mode
  MSR      spsr_el3, x1

  ERET

Where "el2_entry_aarch32" is a label giving the address in EL2 to be entered at.

Thanks for the reply.
But how to set that configuration signal at the time of reset.i want to boot up in AARCH32 bit mode in baremetal code. 

Regards
Rana.

Check you SoC description if the signal is available. If not, just boot in AArch64 and switch.