cpu/x86: Add function to set `put_back_original_solution` variable

`put_back_original_solution` variable in mtrr.c is static, but there is
a need to set put_back_original_solution outside of mtrr.c in order to
let `remove_temp_solution` to drop any temporary MTRRs being set
outside `mtrr_use_temp_range()`, for example: `set_var_mtrr()` function
is used to set MTRRs for the ROM caching.

BUG=b:225766934
TEST=Able to build and boot google/redrix.

Change-Id: Ic6b5683b2aa7398a5e141f710394ab772e9775e7
Signed-off-by: Kane Chen <kane.chen@intel.corp-partner.google.com>
Signed-off-by: Subrata Banik <subratabanik@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/63485
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Werner Zeh <werner.zeh@siemens.com>

src/cpu/x86/mtrr/mtrr.c

@@ -860,6 +860,11 @@ void x86_mtrr_check(void)
 
 static bool put_back_original_solution;
 
+void need_restore_mtrr(void)
+{
+	put_back_original_solution = true;
+}
+
 void mtrr_use_temp_range(uintptr_t begin, size_t size, int type)
 {
 	const struct range_entry *r;

src/include/cpu/x86/mtrr.h

@@ -96,6 +96,7 @@ void x86_setup_fixed_mtrrs(void);
 /* Set up fixed MTRRs but do not enable them. */
 void x86_setup_fixed_mtrrs_no_enable(void);
 void x86_mtrr_check(void);
+void need_restore_mtrr(void);
 
 /* Insert a temporary MTRR range for the duration of coreboot's runtime.
  * This function needs to be called after the first MTRR solution is derived. */