Fix to solve the failing tests shamt, csr and scall (#151)

* making mtvec_handler global

* Adding the pmp configuration inst

The PMP config instructions are added as the test jumps to user mode

* Adding pmp config inst

Adding pmp config instructions as the test jumps to user mode

* changing to PMP macros

* changing to PMP Macros

* moving the #endif after pmp initialization

* Removing the unwanted label